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Clearing Muddy Ponds

By Kenneth Williams

Turbid or muddy water is a common problem for many pond owners. Muddy water is unpleasing to the eye and more importantly, it reduces fish production and fishing success. Turbidity reduces light penetration into the water column and consequently, lowers natural production of fish food items in the pond. Sunlight provides the initial energy for photosynthesis that powers production of phytoplankton, the microscopic plants at the base of the food chain. Less food availability results in fewer pounds of fish per surface acre of pond.

Angling success is reduced in turbid ponds because there are fewer pounds of catchable-sized fish due to low productivity; and it is more difficult for fish to find artificial lures. Many sportfish including largemouth bass, bluegill and other sunfishes are sight feeders. Fish that rely on vision to find food are less successful in muddy ponds.

Why are ponds muddy?

Muddy ponds are usually caused by one or a combination of factors.

1. Extremely small electrically charged clay particles from sediments become suspended in the water. Much of their movement is controlled by negative electrical charges on the particle interacting with positive charges from the water. Negative electrical charges on the clay particles and the surrounding cloud of positive charges from the water causes particles to repel each other. The electrical charges prevent clay particles from clumping together and forming larger particles that can more readily settle to the pond bottom.

2. Another common cause of turbid water is sediment laden water entering the pond from the watershed, usually during heavy rain events. Sediment may come from eroded fields, construction sites or sediment laden streams.

3. Aquatic organisms can cause turbidity in ponds. Common carp, bullhead catfish or other fish species are continually stirring pond bottom sediments. Bottom feeding fish often stir the pond bottom as they sift out organic debris, insects and other food items found on the pond bottom. Nesting activities of many fish species also can stir bottom sediments in shallow (less than 4 ft.) water.

4. Wind commonly causes turbidity in many Oklahoma ponds. Long shallow ponds in treeless, exposed areas, oriented on a north to south axis are most prone to wind produced turbidity. Bank erosion is often severe in these ponds.

5. Cattle and other livestock cause turbidity in many farm ponds. Livestock trails to the pond are a source of erosion. Eroded cattle trails cause extensive damage to pond dams and can cause eventual failure of the dam. Cattle are often found standing in ponds throughout the hot days of summer. Their hooves stir and trample the pond bottom creating a muddy, poor quality fishing pond.

Due to livestock needs or unalterable environmental conditions It is not always possible to remedy causes of turbidity. it may be best to stock fish that thrive in muddy ponds. Channel catfish, hybrid bluegill and fathead minnows are good species choices for the chronically muddy pond. Fish stocked into muddy ponds should be fed. Natural productivity is low and natural food supplies are not adequate to support a healthy fish population without supplemental feeding.

Clearing muddy ponds

Determine the cause

Determine sources of turbidity before deciding on a treatment. Begin by taking a water sample. Use a clear glass jar. Place the jar containing the water sample in a location where it will not be disturbed. Check the sample after 1 week. If the water has cleared, the turbidity is probably caused by fish, other aquatic organisms or wind action. Eroded material from the watershed entering the pond could also be a cause. If the water remains muddy after remaining undisturbed for 1 week, turbidity is caused by suspended colloidal clay particles. The clay may come from pond bottom sediments or from eroded material in the watershed.

Watershed erosion

Regardless of the test results determined above, check the surrounding watershed and repair eroded areas. If watershed erosion is not prevented, each rainfall will add additional sediments to the pond and it will become muddy again resulting in wasted time, effort and expense in pond treatments. Maintain a vegetated ground cover for a width of at least 100 feet around the pond.

Wind

After watershed erosion problems have been eliminated as a cause of pond turbidity, consider wind and wave action as a possible cause of muddy water. Shallow windswept ponds are often muddy for this reason. In the short term, little can be done to adequately remedy this situation. Chemical or hay treatments may clear the pond for a short time but it will become muddy again with the next windy day.

Wind caused turbidity can be reduced by spreading rip-rap or large diameter, crushed rock on shorelines receiving the most wind. Rip-rap placed on wind eroded dams and levees can prevent dam failure and consequent loss of the pond.

Windbreaks planted against prevailing winds can be a good long term solution for turbidity problems. Trees can also be planted around the pond except on the pond dam. Never plant trees on the pond dam. Tree roots are a common source of leakage and dam failure.

Livestock

Livestock are often the obvious cause of erosion and stirred bottom sediments in the pond. It is of no use to clear a pond used by livestock. The only practical method of clearing a muddy pond used by livestock is to fence out the animals and use a water device below the dam or as a compromise, fence the pond to allow very limited access in a specially prepared area of the pond. Making a ramp of road gravel that extends into the pond can reduce turbidity problems somewhat. However, in most ponds, the gravel is quickly pushed deeply into the pond mud. This practice is best used in ponds with a firm bottom.

Bottom feeding fish

If pond water has cleared in the water test and erosion, wind and livestock have been eliminated as causes for turbidity, examine the pond for bottom feeding fish. Common carp and bullhead catfish are the most likely fish causing ponds to become muddy. Fishing with dough balls or catfish baits are the easiest ways for most pond owners to determine if numbers of these fish are present. Seining a portion of the pond can also catch these fish readily.

Remove all carp and bullhead catfish caught in the pond. If the pond is filled with large numbers of stunted bullhead catfish and carp it may be necessary to reclaim the pond and restock with appropriate fish species.

Clear the pond using turbidity treatments described below after nuisance fish have been removed.

Clay turbidity

Suspended clay particles are the cause of turbidity if the test sample remains muddy after standing for a week undisturbed. Clay may become suspended by activities of bottom feeding fish, wind or watershed erosion. Regardless of the cause, the particles will not settle out of the water column even after the initial cause of turbidity is corrected. The pond must be treated to reduce turbidity. Use one of the treatments listed below to clear the pond.

Treatment methods to clear clay turbidity from ponds

Hays

Alfalfa, clover or bermuda hay applications are least expensive and often most practical method of clearing muddy ponds. Organic acids produced as the hay decomposes provide positively charged ions that neutralize negatively charged clay particles and allow them to settle to the pond bottom. Hay takes more time than chemical applications to clear muddy ponds; and hay treatments may need supplemental gypsum applications in some ponds. However, used at recommended rates, hay clears ponds of excess turbidity and stimulates growth of food organisms that ultimately benefit fish. Gypsum and other chemical clearing agents do not provide this additional benefit.

Hay is best used in ponds with low levels of organic matter. Hay and all organic material uses oxygen from the water as it decays. Too much hay applied to a pond may result in fish kills caused by low dissolved oxygen levels in the water. Reduce hay applications in ponds already containing large amounts of decaying vegetation such as areas of recently killed cattails or other aquatic plants.

Apply hay in late winter to early summer to reduce the possibility of low dissolved oxygen related fish kills.

Before adding hay to the pond, use the vinegar test (fig.1) to determine it’s ability to reduce turbidity.

Application rates:

Pond description: Firm mud bottom soils, no cattle access, no aquatic plants visible, no vegetation in pond, very turbid water.

Apply hay at the rate of 8, 50 lb square bales per surface acre or an equivalent amount of round baled hay. Flake the bales and scatter hay around the edges of the pond in about 1 foot of water. Heel in a corner of the hay flake to help keep it anchored in place. Hay is not effective unless submerged. Apply 1-2 additional bales of hay in 3-4 weeks if necessary. Do not apply more than 1000 lb/acre /year. If the pond has not sufficiently cleared in 4 months, apply a chemical clearing agent, either gypsum or alum as described below. Use test provided to determine application rate.

Pond description: Soft mud bottom, some rooted aquatic plants.

Apply hay at the rate of 3-5, 50 lb square bales per surface acre or an equivalent amount of round baled hay. Apply 1-2 additional bales of hay in 4 weeks if necessary. Do not apply more than 600 lb/acre /year. If the pond has not sufficiently cleared in 4 months, treat with gypsum or alum. Use test provided to determine application rate.

Pond description: Livestock in the pond during the summer or vegetation covering more than 30 percent of surface area.

Do not apply hay. Organic matter is already present in large quantities. Use a chemical clearing agent to clear pond water.

Chemical clearing agents

Chemical clearing agents use positive charged metal ions to bind clay particles together in a floc. Gypsum (calcium sulfate) and alum (aluminum sulfate) are the compounds most commonly used to reduce turbidity in ponds. When using alum or gypsum, follow label instructions and always use a particle mask to prevent dust inhalation.

Alum (aluminum sulfate)

Alum controls turbidity more effectively than gypsum because each aluminum ion provides a 3+ charge; as compared to the 2+ charge of the calcium ion in gypsum. It also costs somewhat less to use, about $75 per 100 lb. However, alum has disadvantages not found with gypsum.

1) Alum is not as readily available as gypsum. It usually must be purchased from a chemical supply company.

2) Most importantly, alum, when used in water with low alkalinity levels can lower pH and increase acidity of the water, possibly to levels lethal to fish. Fish survival and reproduction are reduced below pH 5 but they may die at higher pH levels if the change is made suddenly, as happens when pH lowering chemicals such as alum are added to ponds. Test pond water alkalinity before treating with alum.

Add ˝ pound of hydrated lime to every pound of alum applied to the pond if alkalinity is below 20 mg/l. Hydrated lime will help maintain pH at safe levels. Hydrated lime is available at farm and feed stores at a cost of $4.50 - $5.00 per 40 lb bag.

Application rate

Method 1:

Apply alum at a rate of 125 pounds per surface acre in ponds with a secchi disk visibility of 12 - 6 inches (table 1.). Secchi disk visibility can be estimated by measuring the depth at which a

 

Table 1. Pounds of alum required per surface acre for an average Oklahoma pond based on secchi disk visibility,

   
 

     

Pond Size In Acres

   

Secchi disk

1/4

1/3

1/2

2/3

3/4

1

visibility

           

6 in. or more

30

40

65

85

95

125

6 in. or less

50

65

100

135

150

200

white coffee cup or similar object disappears when lowered into the water.Apply alum at a rate  of  200 pounds per surface acre in ponds with a secchi disk visibility of 6 inches or less.

Method 2: Prepare an alum slurry by adding 2 level teaspoons of alum to 1 gallon of clear water. Take 3 pond water samples in clear 1 quart jars. Add 1 teaspoon of alum slurry to the first 1 quart sample, 2 teaspoons slurry to the second sample and 3 teaspoons slurry to the third sample. Determine the number of teaspoons of slurry needed to clear the water. Use this number in table 2. to select the appropriate application rate.

Table 2. Alum application rate based on slurry test.

No. of teaspoons

Alum application

(lb / acre ft.)

1

30

2

60

3

90

How to apply

Apply alum to the pond in calm weather. Alum must be applied evenly over the surface of the pond and rapidly mixed into the water column. For small ponds, make a slurry of 1 part alum to about 10 parts water and apply to the surface. In larger ponds it is more effective to use a boat with motor and pour the slurry into the prop wash as the boat is guided back and forth across the pond.

Clearing should begin in a few hours and continue for several days.

Gypsum (calcium sulfate)

Gypsum is not as effective as alum but it is often used as a first choice because it is inexpensive and readily available. Cost is usually about $5.00 per 40 lb bag or $200 per ton. Gypsum has the added advantage of being safer to use than alum because it will not reduce alkalinity or alter pH of the pond. However, it is ineffective in hard water. Hard water contains an abundance of calcium (greater than 50 mg/l calcium hardness). If turbid water is already saturated with calcium, addition of gypsum (calcium sulfate) will not clear the water. Alum or hay will be required to remove turbidity from hard water ponds.

Application rate

Begin by testing the effectiveness of gypsum in your pond before spending time and money

on a treatment that may not be suitable (fig 2.).

Gypsum is usually applied at a rate of 250 - 2,000 pounds per surface acre. There are several methods used to calculate the amount of gypsum needed, assuming that test samples show gypsum can clarify the pond.

Ponds clarify at varying rates from over night to up to 4 weeks or more after application due to differences in water chemistry, weather conditions and water currents. Very muddy water may clear more rapidly than less turbid water.

It may be necessary to reapply gypsum annually at a rate of 50-100 lb / acre to maintain clarity.

Do not add gypsum to a clear pond. Phosphorus, an element necessary for phytoplankton growth, will be removed from the water and unneeded calcium hardness will be added.

Method 1:

Apply 500 lb gypsum / surface acre. If the pond remains turbid after 4 weeks, apply an additional 125 lb gypsum / surface acre. This treatment is effective in many ponds. It’s main advantage is that only surface area of the pond is needed to determine application rate. This method is not recommended for ponds larger than about 2 acres or deeper than 12 feet.  Test pond water before beginning gypsum applications to insure that it will reduce turbidity in your pond.

Application rate can be determined more accurately if average pond depth is known. Average pond depth can be found by measuring pond depth at 10 - 20 locations in the pond. Average pond depth is calculated by adding all sample depths and dividing the resulting number by the number of samples taken. Average depth also can be estimated by multiplying the maximum pond depth by 0.4.

Gypsum application rate per surface acre based on average pond depth can be found in table 3.

Table 3. Pounds of gypsum required per acre based on pond depth.

     

Pond Size In Acres

   

Avg. Depth (ft.)

1/4

1/3

1/2

2/3

3/4

1

2

260

350

520

700

780

1050

2.5

330

440

650

870

980

1310

3

390

520

780

1040

1180

1570

3.5

460

610

900

1220

1370

1830

4

520

700

1040

1390

1570

2090

4.5

590

780

1180

1570

1760

2350

5

650

870

1310

1740

1960

2610

5.5

720

960

1440

1920

2160

2870

6

780

1040

1570

2090

2350

3140

Method 2:

Use secchi disk visibility to determine application rate. Suspend a white coffee cup from a string. Lower the cup into the water and measure the depth at which it can no longer be seen. Apply gypsum at rates indicated below:

Secchi disk visibility is 6 inches or less, apply gypsum at a rate of 2,000 lb / surface acre.

Secchi disk visibility is about 12 inches apply gypsum at a rate of 1,000 lb / surface acre.

Secchi disk visibility is more than 12 inches apply gypsum at a rate of 250-500 lb / surface acre. Water with visibility in excess of 15 inches may not require treatment.

Method 3:

Water testing to determine application rate. This test is easy to perform, can save the expense of buying more gypsum than needed and is more accurate than previous methods.

1. Place 2 level teaspoons of gypsum in 1 quart of tap water.

2. Fill 7 quart jars with pond water. It helps to label the 6 test jars 1-6.

3. Place 1 quart jar of pond water aside for later comparison.

4. Stir or shake the gypsum and water mixture throughly. (A kitchen mixer works well.)

5. Immediately measure 1 tsp. of gypsum slurry into the first jar and stir. Continue by adding 2 tsp. of slurry into the jar labeled 2. Repeat the process through jar 6 which should contain 6 teaspoons of slurry in the quart jar of pond water.

6. Allow the 6 test jars and the comparison jar of water to stand undisturbed for 12 hours.

Important - For consistent results, continuously stir the slurry as it is used. Gypsum will settle to the bottom of the jar if it is not stirred.

Interpreting results

Each teaspoon of slurry equals a gypsum application rate of about 150 lb of gypsum per acre foot of water. Application rate is determined by choosing the lowest gypsum concentration that clarifies the water. For example, if jar 4 (4tsp. of slurry) remained turbid but jar 5 (5 tsp. of slurry) was clear, gypsum should be applied to the pond at the rate indicated by jar 5.

If no water sample clears after 12 hours, consider another method of turbidity reduction.

Use table 4. to determine application rates based on acre feet of water.

Avg. pond depth x lb of gypsum / acre ft = application rate per surface acre.

Table 4. Gypsum application rate based on slurry test.

No. of teaspoons

Gypsum application

(lb / acre ft.)

1/2

75

1

150

2

300

3

450

4

600

5

750

6

900

Use table 5. to determine application rate when average pond depth is not known.

Table 5. Pounds of gypsum required per surface acre for an average Oklahoma pond based on slurry test results.*

 

   
     

Pond Size In Acres

   

No. tsp. Slurry

1/4

1/3

1/2

2/3

3/4

1

1/2

70

90

135

180

200

270

1

135

180

270

360

405

540

2

270

360

540

720

810

1080

3

405

540

810

1080

1220

1620

4

540

720

1080

1440

1620

2160

5

675

900

1350

1800

2025

2700

6

810

1080

1620

2160

2430

3240

 

*Application rate Based on average pond depth of 3.6 ft.

How to apply

Gypsum can be applied from a boat by sprinkling the compound over the water surface with a shovel. Even coverage is required for effective application. Better mixing can be obtained using a 1 part gypsum to about 10 parts water slurry poured into a boat motor prop wash as the boat is maneuvered around the pond. Better mixing results in more efficient turbidity reduction. If no water sample clears after 12 hours, consider another method of turbidity reduction.

 

 

 

 

 

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