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Black Hawk Lake ahead of schedule in wake of fish kill

Black Hawk Lake ahead of schedule in wake of fish kill

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LAKE VIEW, Iowa | For the first time in four years, Black Hawk Lake enters spring with a exciting development: Water is going over the spillway, a sign the lake is at full-pool.

"We reached full-pool in July and have been flowing over ever since," says Ben Wallace, fisheries biologist for the Iowa Department of Natural Resources. "The soils finally got saturated."

Funny what a wet summer will do, beyond breaking a dry spell.

Wallace is excited to see activity continue to bounce back, or make waves, on this 922-acre lake, a recreation and tourism draw for Sac County. One year ago, Wallace predicted this would be the year when all sorts of 15-inch fish would flourish in the wake of an intentional fish kill that eradicated the lake of all fish, especially unwanted rough species on Nov. 8, 2012.

A drought that summer had reduced the lake's volume by 45 percent, giving DNR officials their chance to apply the toxicant rotenone to kill off organisms with gills, as the substance is taken up through the gills and interrupts the flow of oxygen.

The aim was to one day improve water quality and habitat by eliminating rough fish like carp and gizzard chad that had sucked the vitality from a body of water that annually attracts 150,000 users.

"There was a week last fall where fishers did really well, catching limits for perch and bluegill in the eigth- to nine-inch ranges," Wallace said. "We then had some perch and walleye caught in the first week of ice fishing, although the ice wasn't real good until late December or early January."

The ice went out of Black Hawk Lake one week ago. Wallace predicts spring anglers to return as the weather warms.

"I'm hoping to see decent walleye, bluegill and channel catfish numbers," he said. "We still need to build up those catfish numbers, though."

As the ice was going out last week, the water clarity looked good, far beyond the 6-inch water clarity that Black Hawk Lake averaged three years ago.

Native vegetation continues to grow, which is a postive.

"We want vegegation to grow at the inlet, as it intercepts water from the watershed before it reaches the main portion of the lake," Wallace said. "If you slow water down, it drops off sediments and phosphorous often attaches itself to vegetation in the inlet."

Overall, that helps the health of the main lake.

The 162-acre inlet at Black Hawk Lake has an average depth of 1.6 feet. This summer, the DNR plans to place an hydraulic dredge on the inlet to remove 400,000 cubic yards of sediment, material that will be dumped into an old spoil site used in the 1990s.

Additionally, the DNR will dredge the marina area in the fall, removing 7,200 cubic yards of sediment.

"There are 20 public docks for people to fish from there and the work should also improve the boat ramp and boat access there," Wallace said.

Black Hawk Lake's deepest point is 13 feet. The average depth comes to 6 feet.

"If we can increase the inlet depth to 3 feet, we can achieve a 60-percent reduction of phosphorous delivery to the main portion of Black Hawk Lake," he concluded.

By 2017, Wallace said, Black Hawk Lake should reach its carrying capacity.

"We were hoping for harvestable-sized fish in three years (from 2012) and we've exceeded that," Wallace continued. "We saw lots of harvested fish last year. We've seen 19-inch-plus walleye, though there aren't many of those."


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