Page 3 - VLA Newsletter Fall 2022

Whew! No Zebra Mussels found in Lake Vermilion this year!
Anews release on August 1 by the Minnesota Department of Natural Resources reported a fishing guide snagged an adult zebra mussel
on Lake Koronis outside of Paynesville in Stearns County. Lake Koronis gained notoriety in 2015 for being the first Minnesota lake in which starry stone-
wort, a highly invasive algae, was also discovered. While zebra mussels have not been found in Lake Vermilion, their northern advance has continued as evidenced by a growing list of area legacy mine pits where they are now found. Lake Ore-Be-Gone by Gilbert, a busy recreation area for sport fisher- men, kayakers and divers, was placed
on the infested list in 2012. Boats are checked and there is an on- site decontamination unit. In 2021, zebra mussels were found in the St. James Pit ad- jacent to Aurora and this year in the Embarrass Mine Pit (also known as the Sabin Mine Pit) outside Biwabik and the Canisteo Pit adjacent to the cities of Bovey and Taconite. Both mines are stocked with stream trout and other fish species making them popular with anglers. In addition to the ecological impacts zebra mussels have on a waterbody, zebra mussels can cause expensive damage to water intake pipes reducing or blocking flow. Water containing zebra mussel larvae, called veligers, must be filtered and/or treated to eliminate veligers before it can be used for drinking water or discharged to prevent the spread of downstream receiving waters.
Zebra mussels thrive in slightly alkaline, nutri- ent-rich water which supports healthy populations of plankton and has substantial levels of calcium re- quired for shell development. The lakes of northeast- ern Minnesota are on a geologic feature known as the Canadian Shield, a large area of exposed igneous and high-grade metamorphic rocks. As a result,
they tend to have low calcium levels unlike lakes located on limestone formed by ancient sea beds. It is thought that calcium levels of at least 20 mg/liter
is required for zebra mussel larvae to survive into adulthood and form a reproducing adult population.
Due to differences in
local geology, many
of the area mine pits
have calcium levels
well above 20 mg/
liter making them
an ideal nursery for
zebra mussels. The
Sportsmen’s Club of
Lake Vermilion, now
known as the Ver-
milion Lake Associ-
ation, started moni-
toring calcium levels
in 2015 and noted
levels around 25-30
mg/liter in East Two
River above the Tower harbor. Historically Vermil- ion’s highest calcium levels are about 13 mg/liter in the east basin gradually falling off traveling west. The East Two River and Tower harbor have been consid- ered a potential “hot spot” for zebra mussel develop- ment and intermittent monitoring of calcium levels as well as screening for veligers have continued over the years.
Sources for the increased levels of calcium noted
in East Two River include water from Eagle’s Nest which flows into Vermilion, Tower’s settling ponds, and discharge from the Soudan mine. In a recent analysis, water from the mine gathered at Soudan’s monument culvert noted a calcium level of 327 mg/ liter. However, measurements noted downstream significantly decreased to 19 mg/liter as it entered Pike Bay. The higher calcium level of the area is still a concern. As a result, the AIS team of the VLA has placed four sampler plates in the harbor and along the river and conducts a yearly tow screening for veligers. With good boating and fishing practices, remembering to clean, drain and dry, it is hoped that East Two River does not become another zebra mussel nursery.
Nancy Watkins VLA Board Member/ AIS Co-Leader
www.VermilionLakeAssociation.org 3