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Project Underway to Turn Around Lake Pahoja
Posted: 04/12/2013
The fishery at Lake Pahoja was renovated on April 4, to remove common carp and grass carp that caused poor water quality and frequent algae blooms. For the first time since 1979, the lake will get a fresh start.

Lake Pahoja experienced a significant fish kill last fall after oxygen dropped to dangerously low levels throughout the lake.  A combination of a very large algae bloom and the annual fall lake turnover likely caused the die off.  The kill impacted many fish species and was a sign of an out of balance fishery and unhealthy lake.

It is very unusual for a lake fish kill to occur in the fall and confirmed what was known for some time, said Mike Hawkins, fisheries management biologist for the Iowa Department of Natural Resources.

“Lake Pahoja has not been as healthy as it should be. The frequency and intensity of the algae blooms the lake had been experiencing indicate an excess in nutrients and lack of rooted aquatic plants,” he said.

Excessive nutrients in lakes come from the land that drains into them. Once those nutrients are in the lake, an out of balance fishery can cause productivity to go haywire. 

Common carp feed by rooting up the bottom of a lake causing water clarity problems and releasing nutrients tied to those bottom sediments.  Grass carp feed on rooted aquatic plants.  With more than 100, 40-to 60-pound grass carp in the lake, aquatic plants have never been seen.

Aquatic plants are important because they create critical habitat for fish and invertebrates and improve water quality by taking up nutrients that keep algae blooms to a minimum.

“With these two species gone, the water should clear up and we should begin to see aquatic plants grow along the shoreline creating a ‘weed line,’” Hawkins said. “This should help create a much more balanced fishery.”

Panfishing had been poor for a number of years, said Craig Van Otterloo, executive director for the Lyon County Conservation Board.  “With a brand new fishery, we know that is about to change. Lake Pahoja is a very important part of this county and we want it to be the best it can be,” Van Otterloo said.

The Lyon County Conservation Board secured a County Fish Habitat Grant to pay for the renovation. 

“Drought conditions allowed us to draw the lake down about 5 feet dramatically reducing the amount and cost of the chemical to be applied,” said Van Otterloo.

Crews worked for two days with the DNR’s electrofishing boat before the renovation to salvage nearly 800 largemouth bass that were placed in county ponds.  Some are being held in one of the park’s ponds and go back to Pahoja when the lake is ready to be restocked in a 2-3 weeks.

The chemical, called Rotenone, was used to renovate the fishery because it kills fish quickly without harming other organisms.  County Conservation Board staff began picking up larger dead fish from the shoreline shortly after application.  A significant number of the larger fish were common carp.  Dead fish were applied to a local crop field and incorporated as fertilizer.
Hawkins says the lake will receive 48,000 one-year-old bluegills towards the end of April, followed by about 70 adult largemouth bass. Channel catfish will be stocked next June. Other species will be considered after bluegills and largemouth bass are well established.

“The growth rate of the fish stocked this spring will be extreme. We can expect good fishing for bluegill by the end of next summer, with bigger fish by the following summer,” says Hawkins.

Van Otterloo says it is extremely important that anglers do not release live fish or minnows into Lake Pahoja.  Not only is it unlawful to do so, an illegal stocking will jeopardize the fishery.

The Lyon County Conservation Board and the Fisheries Bureau of the Iowa Department of Natural Resources cooperated on this project.

For more information, contact Mike Hawkins, Fisheries Biologist, Iowa Department of Natural Resources, 712-336-1840.