As part of the 2020 Virtual Ag Progress Days, a panel of Penn State Extension experts provided a webinar about the ecology and function of small- to medium-sized earthen ponds. They provided basic information about managing ponds between a quarter-acre and 5 acres in size.
Extension educator Peter Wulfhurst discussed common pond concerns, pointing to the benefits of good pond maintenance. This involves conducting an annual inspection for things like bank erosion and early signs of leaks. Removing small trees along the dam, checking the outlet pipe, maintaining the dry hydrant, if any, and inspecting any fencing present should also be part of the inspection process.
If a drop in pond water level is observed, Wulfhurst indicated that such conditions are typically due to seepage, evaporation and/or leakage. The best way to avoid pond leakage is through proper initial construction, because addressing leaks later is an expensive proposition. Draining a leaking pond to install sealing products might be necessary; this may involve compacting existing clay, adding more clay or introducing other sealants like bentonite or plastic.
When constructing or performing maintenance projects on a pond, it’s important to consider permit requirements, said Wulfhurst. Permits are typically unnecessary for stocking fish (other than grass carp), aeration, physical control measures (with the exception of dredging or drawdown), barley straw applications or bacteria/enzyme applications. Checking with the local conservation district is the best way to determine if the proposed work requires a permit.
Water quality is another determinant of pond condition. Knowing pH value; bacteria; total dissolved solids; nitrate, phosphorous, sulfate, iron, manganese and aluminum levels; hardness; and alkalinity are important to pond health. Being aware of water temperature and dissolved oxygen content is also helpful. Wulfhurst explained that having pond water analyzed is an essential step, not only for diagnosing current pond problems, but also for preventing them in the future. Pond and lake water test packages are available through Penn State’s accredited water laboratory (for further information, see agsci.psu.edu/aasl/water-testing/pond-and-lake-water.)
Algae issues are the most common pond-related complaints. Wulfhurst pointed out that addressing this concern requires understanding algae’s important role in a pond’s food web. Fish eat small insects, and small insects’ diets include phytoplankton, single-cell, free-floating, non-swimming plants, such as algae. Sunlight exposure causes algae to proliferate and, when algae exceeds the ability of their environment to consume them, a troublesome overgrowth results.
Extension educator Susan Boser went into greater detail on algae control, re-emphasizing that algae are not all bad. Problems occur when sedimentation decreases pond depth and nitrogen and phosphorous inputs become too great. She talked about how aging ponds come to have excessive nutrients and sediment, which in turn leads to shallowness, loss of species diversity, too much or too little aquatic plant life, low dissolved oxygen levels, high dissolved metals levels, noxious odors and algal blooms. The development of these conditions is called “eutrophication.”
Ponds less than 5 feet deep that experience surface runoff are twice as likely to have algae as other ponds. Penn State offers free pond water testing specifically designed to address nuisance aquatic plant and algae problems. (See “Penn State Addressing Nuisance Algae” for further details.)
Boser stressed that pond owners should strive for a diverse mixture of aquatic plants in their ponds, as well as emergent plants, such as cattails along the pond’s edge. Floating plants like duckweed and water lilies also are good additions. She advised being watchful for algae starting to overtake a pond, noting some are filamentous algae decaying and floating to the top. Other algae occur midsummer to fall, displaying various colors and textures, resembling spilled paint or pea soup. These represent an algal bloom, which can produce toxins dangerous to both animals and humans. Swimming or using the pond water should be avoided for two to three weeks after the bloom disappears.
New plants suddenly appearing in a pond may be exotic invasives, which should be dealt with immediately, before they spread. Nutrient control can prevent unwanted aquatic plants and algae with these tactics: creating buffers; forming a sediment pond; providing appropriate septic system maintenance to avoid contamination; aeration; reducing use of fertilizers and related run-off, which encourages aquatic plant growth; stabilizing pond banks to avoid sediment; and controlling animals like Canada geese, whose droppings contribute significant amounts of nutrients.
Boser reviewed mechanical controls on aquatic growth, such as dredging to deepen a pond, as well as raking and pulling underwater plant life, drawing down the pond or using a special harvester to remove unwanted pond vegetation. She cautioned that pond owners should sure to remove the resulting plant debris away from the pond.
Biological control of aquatic plants can be achieved using sterile triploid grass carp, which require a permit; applying barley straw to the pond in winter or early spring; or using bacteria or enzymatic products, which are pricey and can take over a year to see results, but are effective.
Aquatic herbicides are another option, but these require permits and can only be applied to half of the pond at a time so that the resulting oxygen removal doesn’t kill fish. They are best used when an algal bloom first appears.
Brian Swistock, senior water resources Extension associate, spoke about utilizing ponds to attract wildlife and sustain fish. He noted the popularity of pond denizens like turtles, frogs, wood ducks, kingfishers and red-winged blackbirds, and summarized, “if you build it, they will come.” Plans for bat boxes, duck boxes, and other types of species-specific shelters are available online. Using rocks along the pond’s edge attracts amphibians and reptiles.
The trick, Swistock said, is not to attract species you don’t want. The most unwanted species is Canada geese. Bacteria-carrying droppings in and around ponds, as well as their sometimes-aggressive behavior during mating season, makes these birds undesirable pond guests. Swistock recommended the use of buffers, such as tall grasses, around the pond to discourage this ground-nesting species, which is nervous about unseen predators.
“Geese like lawn grass, so plant other things,” advised Swistock. Allowing winter ice and using scarecrows are also deterrents.
Muskrats are another animal to discourage from ponds, as their excavations cause leaks. Swistock suggested avoiding the use of cattails in pond areas, and rip-rapping the shoreline from 1 foot above to 3 feet below the water surface with large gravel if muskrats are a concern.
Swistock explained that fish habitat creation requires planning and monitoring. Pond water usually isn’t cold enough for trout, unless they are stocked in cool weather months and fished out by mid-June. A combination of bass and bluegills is the most successful pond fish option; the ratio of these species depends on the age of the fish stocked. Channel catfish can also be stocked with bass; however, bullhead catfish are to be avoided since they “muddy up” ponds.
Some fish kill is unavoidable, such as the day after heavy rains, when the sudden run-off results in a loss of oxygen. Oxygen may also be depleted by decaying plant and organic matter. Pesticide drift or improper application of aquatic herbicides is another cause of fish death, as are diseases and injury. To avoid winter-kill in shallow ponds with persistent ice and snow, Swistock urged shoveling snow from the ice in a few locations to permit light to enter.
For further general information on ponds, go to https://extension.psu.edu/water/pond-management.