Invasive starry stonewort threatens Big Detroit, Big Cormorant and other Becker County lakes

February 10, 2020

Zebra mussels may get most of the attention when it comes to aquatic invasives, but the unchecked growth of starry stonewort can really jam up a lake, and Big Detroit and Big Cormorant are in the top 10 lakes in Becker County most threatened by it.

“Starry stonewort is more of a problem than zebra mussels, in some lakes it’s a big problem,” said Karl Koenig, the quality and aquatic invasive species coordinator for the Becker Soil and Water Conservation District. Starry stonewort crowds out native vegetation in lakes, and it tends to flourish in shallower lakes like the ones in Becker County, he said.

Starry stonewort can form a dense carpet of material in shallow areas, and it’s a macro-algae, meaning it does not have a vascular system like true plants. Each branchlet or stem is a single cell. That makes it more difficult to kill.

Hoping to get a jump on any infestation, the Becker Soil and Water Conservation District will monitor at-risk lakes for starry stonewort this summer, Koenig said.

He reported on the battle against aquatic invasives at the Becker County Board meeting Tuesday, Feb. 4.

“If you can get it in a localized area, you have a chance to eradicate it,” Commissioner Barry Nelson said.

“Management costs will be less if you treat one acre as opposed to 100 acres,” Koenig agreed. “The costs go up real quick when you’ve got 100 acres of this.”

Monitoring could prove valuable, and “I’m going to get some eyes on these access sites as much as possible in 2020,” Koenig said.

In all, the Becker Soil and Water Conservation District spent just over $351,000 last year on its Aquatic Invasive Species Program, according to a report presented by Koenig. The bulk of that, about $247,000 went to pay its 33 watercraft inspectors at public accesses.

Among other things, they found that over 15% of boats were entering a lake from infested waters. Three percent of boats carried hanging plants, mud and lake water.

Becker County did 366 hot water boat decontaminations last year, with services offered at Detroit, Melissa, Sallie and Big Cormorant lakes.

“In 2020, decontamination services will again be provided at high-use zebra mussel-infested lakes,” the report states.

Using a risk model developed by the Minnesota AIS Research Center, the top 25 lakes in Becker County predicted for starry stonewort invasion are being targeted for monitoring and management.

The lakes are Big Sugarbush, Buffalo, Cotton, Floyd, Height of Land, Ida, Island, Leif, Little Cormorant, Little Floyd, Little Toad, Long, Melissa, Middle Cormorant, Pickerel, Rock, Round, Shell, Straight, Tamarack, Toad, Two Inlets, Upper Cormorant, White Earth and Wolf (not to be confused with the Wolf Lake in Hubbard County that already has starry stonewort).

The Becker County lakes were checked in August and September and “no starry stonewort or other invasive plants were observed in 2019 following approximately 100 hours of sampling,” Koenig said in the report.

The risk model lists Big Cormorant as the second-highest risk lake and Big Detroit as the seventh-highest risk lake for starry stonewort in the county.

Because of the increased risk, scuba surveys were done last year on five primary public access sites on the two lakes.

That was in addition to a search by volunteers of 14 lake accesses on Straight, Sallie, Melissa, Detroit, Lief, Big Cormorant, Cotton, Tamarac and Long. So far, so good on starry stonewort.

Three $4,000 grants were given last year to treat over 11 acres of flowering rush along the Detroit Lakes public beach, 43 acres of flowering rush on Lake Sallie and 35 acres of curly-leaf pondweed on Toad Lake.

The 2020 budget for AIS prevention is set at $382,000, with $343,00 of that coming from the state. It will be used for outreach, education, boat inspections, decontamination, lake monitoring and treatment.