The fish upset the native ecology and lower water quality, so neighboring communities hired fishermen to remove them.
Professional fishermen pulled more than 4,000 pounds of carp out of Silver Lake in a single day in January. It would have been upward of 10,000 pounds — nearly the lake’s entire carp population — if the net hadn’t snagged and ripped.
Ridding the lake of the species and improving water quality is the goal.
Silver Lake, which straddles the border of Anoka and Ramsey counties, was designated as having “impaired” water (fails to meet one or more water quality standards) by the Minnesota Pollution Control Agency more than a decade ago.
Its shoreline neighbors — Three Rivers Park District, Rice Creek Watershed District and the cities of St. Anthony, New Brighton and Columbia Heights — have partnered to improve the lake’s water quality. They have pooled together $30,000 to pay for the effort, including carp removal, which started this winter.
A water-quality study recommended that most carp be removed from the lake.
“One of the improvements mentioned is removing the carp because they consume all the vegetation in the lake,” said St. Anthony city engineer Todd Hubmer. “They also stir up the bottom of the lake. It makes it cloudy and it stirs up the nutrients into the water column, which makes algae grow. None of the carp species are native. They swim up ditches and channels. They will get transported by fishermen or in minnow buckets.”
The carp also upset the native ecology, Hubmer said. Bluegills, crappies, perch and largemouth bass feed on carp eggs and minnows instead of zooplankton and other native food sources.
The process of removing the carp actually started last spring. Biologists caught seven of the fish and surgically embedded radio transmitters in their bellies. They then tracked them throughout the year.
Carp typically school under the ice in midwinter. When the transmitters showed they were schooling, professional fishermen scrambled within 24 hours to remove them with a large net. They drilled holes in the ice and strung a net using a remote-control submarine.
About 400 carp, averaging about 10 pounds apiece, were harvested; that’s about 40 percent of the lake’s carp population. Hubmer said the operators believed they had nearly 1,000 fish in the net, but it snagged and ripped on an unknown object on the lake bed.
Native fish caught in the net were tossed back into the lake.
The carp were sent to factories for processing. Carp is used in pet food and fertilizer and is sometimes flash-frozen and sent to other parts of the world for human consumption, Hubmer said.
Carp removal is just part of a bigger plan to improve water quality at the 72-acre lake, which also has high levels of phosphorus. The neighboring cities have worked to control runoff with improved stormwater ponds, basins and rain gardens.
The lake was declared an impaired water body in 2002 because excess nutrients affect swimming and fishing. Substances such as phosphorus from stormwater runoff create frequent summer algal blooms that limit recreational activities.
Silverwood Park, managed by Three Rivers Park District, occupies about half the lake’s shoreline. This is Three River’s first participation with a carp harvest.
“You are trying to knock back the population enough so they are not a significant impediment to getting a healthy system,” said Rich Brash, senior manager of water rescue for Three Rivers.