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That’s A Lot Of Carp!

By Staff | Jul 13, 2010

For the past six years, residents of the Ruthven and Lost Island Lake area have had the unwanted distinction of having Lost Island Lake being named to the Environmental Protection Agency’s nationwide list of Impaired Waters. Lost Island, which lies about two miles north of Ruthven, straddling the Palo Alto and Clay County lines, is a shallow, natural lake formed in the glacial age. At the deepest point, the lake is 15 and a-half feet deep, with an average depth of around 11 feet. Studies compiled by the Iowa Department of Natural Resources are used to make the determination of impaired status, which means the water quality of the body of water has serious concerns for clarity, among other considerations.

While some might think such a designation would be a detriment, it has actually sparked a renewed interest in cleaning up the quality of the lake’s waters. Those efforts are being spearheaded by the Lost Island Protective Association, along with the Palo Alto County Conservation Board, Ducks Unlimited and the Iowa DNR.

When one talks about water quality in a lake that features extensive wetland areas, a major area of concern is increased algae bloom in the waters. Another area of concern for Lost Island is what studies have discovered to be a large population of rough fish – carp and buffalo heads.

According to Mark Gulick, a Fisheries Habitat Specialist out of the DNR’s Spirit Lake Fisheries Bureau, a study completed by Iowa State University showed that the actual watershed of Lost Island Lake was actually in pretty good shape, but that the turbidity problem in the lake itself was due to a huge overabundance of carp in the lake.

Reducing the populations of rough fish has been identified as a key to the restoration of Lost Island.

For the past three years, the Palo Alto County Conservation Board worked with commercial fishing operations to conduct seining operations in the lake, netting some 60,000 carp and buffalo head fish. About 15,000 carp and buffalo were tagged and released for further study, with the rest being sold to the commercial operation.

So, just how do fish affect water quality?

“Carp root around on the bottom of the lake, stirring up the mud and that releases the phosphorus into the water, which promotes the growth of algae and that is what creates the turnover, when the water gets green from the algae,” Gulick explained. “Lost Island just has a huge population of carp. The Fisheries Bureau has determined there are 400 to 450 pounds of carp to the acre in Lost Island. That’s a lot of carp,”

As they root at the bottom of the lake for food, they stir up the sediments at the bottom of the lake, making the waters cloudy. Cloudy water is due to suspended sediments stirred up by the foraging rough fish.

Knowing what causes the problem leads to an answer – Eliminate the fish, reduce the suspended sediments, improve the water quality.

How do you accomplish the solution? You remove the rough fish – to the tune of 400,000 pounds of carp, according to figures supplied by the DNR. An equal amount of buffalo head will also be removed by commercial seining during this year. Work started on the commercial fishing in April, and is currently on hold, as warmer water temperatures create elevated stress for game fish that would be caught up in the nets. To protect the game fish, netting will not resume until the water cools somewhat. To date, approximately half of the DNR’s goal has been netted this spring and early summer.

Once the population of the rough fish has been reduced, other construction will take place at various locations around the lake that provide access to connected wetlands, where the rough fish normally reproduce. A total of five fish barriers are slated to be constructed in the next two years on Blue Wing Marsh, on the east side of Lost Island, as well as multiple locations in the Barringer Slough complex on the west and south west of Lost Island.

Water control structures will also be constructed at the Blue Wing Marsh inlet and the Barringer Slough complex, allowing for the marshlands to be drained down in the winter to help reduce rough fish populations even more.

With conditions made less hospitable for the rough fish, the DNR will also stock more game fish, such as walleye and northern pike, which are natural predators of carp.

But, another concern for the lake is algae bloom, which turns the water green in color in the heat of the summer. Algae blooms are caused by many factors, including phosphorus in the water, and a majority of phosphorus comes through water that comes into the lakes through the watershed. Other factors that affect algae bloom, due to the shallowness of the lake itself, include wind and wave action caused by boats and other pleasure craft. Pollution concerns for the lake were addressed in the late 1980’s when the construction of the Lost Island Sanitary Sewer System around the entire lake, helped to improve quality of the water in the lake. The extensive wetland areas that adjoin Lost Island Lake also act as filtration systems, reducing large amounts of nitrates from ground water that flows into the wetlands and subsequently into the lake.