Assessing Our Risks to Prioritize Our Activities


The resources to completely defend Lake Vermilion’s fishery and business community will never be available. We’re committed to deploying the resources we can muster on our highest priority risks as efficiently as we can.

Those high-priority risks have evolved rapidly over the last couple years. By 2017, starry stonewort – a relative newcomer to Minnesota’s AIS roster – has been found in 6 counties and 11 lakes, including Upper Red, Cass and Winnibigoshish, after its discovery in Lake Koronis in 2015. This grass-like macro algae can produce dense mats, can interfere with recreation, and can alter habitat for young fish. It’s understandable that property values would decrease at lakes and along shorelines with starry.

In the last couple years, hybrid watermilfoil has also made headlines. Little is known about crosses between invasive Eurasian watermilfoil and our native Northern watermilfoil, but anecdotal reports suggest increased invasiveness and evidence of herbicide resistance. In Lake Vermilion, native watermilfoil co-exists with other native vegetation. We have no known Eurasian watermilfoil – an indication our habitat and water chemistry may not be suitable. However, at this point, no one knows whether certain Eurasian x native hybrids may overwhelm our native vegetation.

Zebra mussels, on the other hand, may be a ray of hope. Zebras need sufficient dissolved calcium – about 20 milligrams per liter – to grow and reproduce. Most of Lake Vermilion is below 13 mg/l – well in the safe zone. An exception is East Two River, which flows into Vermilion’s east basin, with calcium above 20 mg/l at certain times of the year. However, its <7.0 pH prevents zebra mussels from becoming established. To be safe, we will continue to monitor east-basin water chemistry for a few years.

Starry stonewort and hybrid watermilfoils are major threats and have moved ahead of zebra mussels at the top of Lake Vermilion’s AIS concerns. Our current risk assessment – including what we don’t know – is summarized below:


Species Introduction Risk Habitat Suitability Impact if Population Established
Fishery & Ecosystem Recreational Boating
Starry stonewort Increasing as more Minnesota lakes become infested. Unknown. Limited to specific bays? Serious stressor. Unknown impact on
each fishery.
Severe in bays with suitable habitat.
Hybrid and Eurasian watermilfoil Very high. Unknown. Limited to specific bays? Serious stressor. Unknown impact on
each fishery.
Severe in bays with suitable habitat.
Zebra mussels Very high. Unknown. Limited to calcium hotspots with suitable pH? Serious stressor. Filters zooplankton, limiting growth of fry. Negative but water clarity appeals to some.
Spiny waterfleas Found in Big Bay
in 2015.
High. Likely to spread beyond east basin. Serious stressor. Consume zooplankton, limiting growth of fry. Low.
Curly-leaf pondweed Present in
3 small areas.
Moderate/high in specific bays. Limited to specific bays with suitable habitat. May become severe in bays with suitable habitat.
Rusty crayfish Present in east basin and west to Niles Bay. High for sandy, rocky, rubble bottoms. Weed bed destruction impacting several
fish species.
Low to moderate.


In addition to the priority threats in the table above, Lake Vermilion is surrounded by a host of other AIS threats which we continually monitor. Examples include quagga mussel, Brazilian waterweed, brittle naiad, and water hyacinth.