Starry Stonewort Infestation Has Spread Across 40 Lakes
The aquatic invasive algae has expanded to Six Mile Lake as Minnesota increases management funding to $1.4 million.
Updated on Sept. 21, 2026 in Botany
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An invasive aquatic algae known as starry stonewort has now been confirmed in 40 Minnesota water bodies. The infestation reached Six Mile Lake in Cass County last week, marking a continued expansion of the species that first appeared in the state in 2015.
Why it matters
The persistent growth of this algae threatens local aquatic ecosystems, forcing the state to increase annual grants for management to $1.4 million. Researchers currently do not know the long-term impact this species will have on water quality, fish populations, and native vegetation.
Controlling the algae remains difficult because it regenerates from star-shaped bulbils left in lake sediment. Lake Koronis, an early site of infestation, spends $170,000 annually to mitigate the growth.
The players
Minnesota Department of Natural Resources
The state agency responsible for overseeing land and water management, including the issuance of permits for invasive species control.
Starry Trek
A volunteer-led program that monitors Minnesota water bodies for invasive species, credited with finding one in four new starry stonewort infestations.
The details
Starry stonewort is a macroalgae that lacks a vascular system, meaning treatments must target every individual cell. Contractors manage the growth by dragging weighted hoses along the lake bottom to apply copper-based algaecides or by using divers to perform suction harvesting, where the algae is pulled from the bottom into floating barge containers. These methods provide only temporary reduction of the biomass.
Timeline
2015: First Minnesota starry stonewort infestation confirmed.
2017: Starry stonewort discovered on Grand Lake.
Last year: DNR issued 482 total invasive species permits.
Last week: Six Mile Lake infestation confirmed.
Current year: DNR grant funding increased to $1.4 million.
The Tech Race
Management of this algae follows the broader pattern of invasive species control in the Great Lakes region, where manual extraction and chemical intervention have largely failed to eradicate established populations. The state's effort relies on the Starry Trek volunteer program to detect outbreaks while researchers continue to assess the feasibility of long-term biological controls.
Residents and lake users in Minnesota should note that management measures like copper-based algaecide and suction harvesting are only temporary solutions. The presence of starry stonewort in 40 lakes requires continued vigilance from the public to prevent spread to unaffected waters.
The takeaway
The spread of starry stonewort highlights the limitations of current mechanical and chemical control methods, which only offer short-term suppression. Residents should monitor the Minnesota Department of Natural Resources grant reports to track how the $1.4 million in annual funding is allocated for future mitigation.
Further reading
Learn more about the latest management strategies in Minnesota Botany.
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