Don’t mean to carp about the estuary problem, but …

Last summer, members of the Lake Management Planning team and Green Lake School District students teamed up to place 27,000 plant propagules in the degraded estuary. This spring, volunteers prepared and placed 30,000 propagules to continue the multi-year attempt to restore the wetland. submitted photo

by Allison Niescier

A local group is in a neck-and-neck battle with Green Lake’s infamous carp. The team’s goal is to reduce the carp population and gain the upper hand in a critical estuary. If that tipping point is achieved, the estuary can be restored to benefit the lake’s water quality.

A fishing contractor has already removed 102,000 pounds of carp at the lake’s southwest corner this year. The carp blitz is a collaboration between the Green Lake Sanitary District (GLSD), Green Lake Association (GLA) and other members of the Lake Management Planning team.

Carp are a non-native species that migrate from the cool lake to the warm waters of the County Highway K Estuary to spawn during springtime. Once in the cove, their abrupt spawning and destructive feeding movements disrupt the shallow bottom and dump phosphorus-loaded sediment into Green Lake.

A chocolate-covered plume of sediment that flows into the lake from the estuary provides evidence of the carp’s destruction. The plume is loaded with phosphorus, which serves as a fertilizer for lake weeds.

Measurements show that nearly 3,350 pounds of phosphorus flow under the County Highway K bridge annually, accounting for nearly 20 percent of the lake’s entire nutrient loading. This equates to more than 1.7 million pounds of lake weeds generated each year from just one area of the watershed.

“If we’re successful at restoring the County Highway K Estuary, we can make a major dent in detrimental nutrient loading,” explained Stephanie Prellwitz, GLA executive director. “As best we can tell, carp are the number one problem for the estuary, so reducing their numbers means a cleaner Big Green.”

Last year, the team removed 170,000 pounds of carp from the lake and from the County Highway K Estuary, which was enough to fill five semi-trucks. The ongoing strategy prevents dead carp from floating up on its shoreline and increases the likelihood of “flipping” the degraded estuary into a healthy nutrient sponge to improve the lake’s water quality.

“The more carp we can take out of the estuary, the better the chances are that we can reestablish plant growth and restore this vulnerable wetland,” explained GLSD Administrator Charlie Marks.

This year, the team is using a series of proactive management strategies to reduce the negative side effects of spawning season. The carp barrier at the County Highway K bridge is locked from boat traffic during peak spawning season.

“Two years ago, carp numbers were so great, they pressed against the hinged barrier, weighed it down and slipped into the estuary in large numbers. Last year, the LMP (Lake Management Plan) team made adjustments to the carp barrier and gate that ensured the integrity of the carp barrier as a whole,” Marks said.

A commercial fishing contractor is working to remove large quantities of carp from both the lake and the estuary. The contractor sends these carp to a regional fish processing plant as a food source.

The GLSD and GLA will attempt to capture straggler carp in the wetland with four large fyke nets that staff empty on a daily basis throughout the summer.

This spring, volunteers prepared and placed 30,000 native plant propagules, or rootstock, into the estuary.

“Based on our research, we’re trying to reduce the carp population to less than 100 pounds per acre in the marsh. If we can do that, we believe the plants can outcompete the carp. And that’s exciting to our team,” Marks said as he shared his optimism in reaching that goal.

While the team continues to manage Green Lake’s invasive carp population, they ask that those interested in bow-fishing carp take their catch with them. Individuals who do not remove speared carp can be subject to a fine. Any questions regarding bow-fishing regulations can be directed to John Screiber, Green Lake Conservation Warden at 920- 369-6028.

To learn more about current lake management strategies on Green Lake, including carp removal, join the Green Lake Association’s annual meeting on Saturday, June 16 from 9 to 11 a.m. at the Goose Blind Grill & Bar.

Alison Niescier is the project manager for the Green Lake Association, a local not-for-profit that works to improve water quality for Green Lake.