Single zebra mussel confirmed in Lake Harriet

Posted on September 21, 2017

On Friday, Sept. 8, a single zebra mussel was found by a Minneapolis Park and Recreation (MPRB) Water Quality staff member in Lake Harriet. The Minnesota Department of Natural Resources (DNR) has confirmed the find and has added Lake Harriet to the Infested Waters List for zebra mussels. The listing includes the provision that Lake Harriet may be removed from the list if future surveys continue to show no zebra mussels in the lake.

The adult zebra mussel was discovered on a boat cover recovered from the bottom of Lake Harriet. Since its discovery on Sept. 8, MPRB staff has been working with the DNR, the Minnehaha Creek Watershed District (MCWD) and contractors to conduct 67 hours of shoreline, snorkel and scuba surveys. As of Sept. 21, no additional mussels have been found.

"We are thankful that no additional zebra mussels were found during the extended search," said MPRB Superintendent Jayne Miller. "We are also very grateful to the DNR and the MCWD for their assistance and ongoing support in the Park Board's Aquatic Invasive Species efforts."

MPRB staff will continue to carefully monitor Lake Harriet the rest of this season and next year, but the DNR has determined that no treatment is necessary at this time.

Being added to the DNR's Infested Waters List does not impact public use of Lake Harriet. The MPRB's Aquatic Invasive Species (AIS) inspection program, which began in 2012, will continue to inspect boats and watercraft entering and exiting Lake Harriet, Lake Calhoun/Bde Maka Ska and Lake Nokomis through the public boat launches. The AIS inspection program will continue through Dec. 1, or until lakes ice over.

Although only one single zebra mussel was found in Lake Harriet, Assistant Superintendent of Environmental Stewardship Jeremy Barrick cautions that anglers and other recreational lake users need to remain vigilant in stopping the spread of zebra mussels and other aquatic invasive species in Minneapolis lakes and across the state.

"We believe that our extensive AIS program, greater public awareness and more Minnesotans following our state's invasive species laws have helped keep our lakes free of zebra mussels up to now," Barrick said. "However, we also know that it may take years for an infestation to fully develop."

According to the DNR, fewer than 250 of Minnesota's 11,842 lakes, or about 1.8 percent, are listed as infested with zebra mussels. To date, no zebra mussels have been found at Lake Calhoun/Bde Maka Ska or Lake Nokomis.

Whether or not a lake is listed as infested, Minnesota law requires boaters and anglers to:

  • Clean watercraft of aquatic plants and prohibited invasive species,
  • Drain all water by removing drain plugs and keeping them out during transport, and
  • Dispose of unwanted bait in the trash.

Some invasive species are small and difficult to see at the access. To remove or kill them, take one or more of the following precautions before moving to another waterbody, especially after leaving infested waters:

  • Spray with high-pressure water.
  • Rinse with very hot water (120 degrees F for at least two minutes or 140 degrees F for at least 10 seconds).
  • Dry for at least five days.

More information on AIS is available at www.mndnr.gov/AIS 

Frequently Asked Questions

When were zebra mussels discovered at Lake Harriet?
One live adult zebra mussel (0.9 in/23mm) was found on the afternoon of September 8, 2017.

Where on Lake Harriet were the zebra mussels discovered?
One zebra mussel was found on a boat cover that had been recovered from the bottom of the lake.

How many have been found?
One, no additional zebra mussels were found after 67 hours of searching.

What does searching for zebra mussels entail? 
The zebra mussel search included examining suitable habitat and objects for the presence of zebra mussels while wading, snorkeling, and diving in areas of Lake Harriet where the initial zebra mussel was found and where there is suitable habitat for zebra mussel survival. The Minnesota Department of Natural Resources (DNR), Minnehaha Creek Watershed District (MCWD), and two companies experienced in aquatic invasive species (AIS) searches helped MPRB with Harriet search effort.

What other Minneapolis waterways are considered infested?

  • Eurasian Water Milfoil: Brownie, Calhoun/Bde Maka Ska, Cedar, Harriet, Hiawatha, Lake of the Isles, Nokomis, Powderhorn, Wirth
  • Zebra Mussels: Meadowbrook Lake, Minnehaha Creek, Lake Nokomis, Lake Hiawatha, Mississippi River
  • Flowering Rush:  Minnehaha Creek
  • Powderhorn Lake has been removed from the DNR’s infested waters list since Egeria densa has not been found in the lake for more than 5 years after treatment.
  • Various MPRB waterbodies also have common carp, goldfish, curly leaf pondweed, and Chinese mystery snails, but these species are not tracked on the official DNR Infested Waters List.

Is Lake Harriet connected to any other Minneapolis waterways? 
Water flows from Lake Calhoun/Bde Maka Ska to Lake Harriet through a pipe and open channel system; however, water from Lake Harriet never flows into Lake Calhoun/Bde Maka Ska. Water flows out of Lake Harriet through an underground pipe to an open channel that flows to Minnehaha Creek. Water from Minnehaha Creek does not flow to Lake Harriet.

How long has the MPRB performed AIS inspections?
MPRB’s inspection program began in 2012. Prior to this, the DNR performed inspections at Minneapolis lakes as part of their statewide program. The number of hours inspected varied from lake to lake and year to year during the time the DNR inspected at the boat launches. The MPRB’s goal is to inspect 100% of the watercraft leaving and entering the lakes via the boat launches.

What are AIS inspection hours?

2017 Inspection hours are:

May 1 – September 17
Daily:  6 am–10 pm

September 18 – October 9
Daily:  6 am–9 pm

October 10 – November 5
Daily:  7 am–8 pm, Inspector On-Call

November 6 – December 1
Daily:  8 am–6 pm, Inspector On-Call

How many times have AIS inspectors stopped zebra mussels from entering the Minneapolis Lakes?
Zebra mussels visible to the naked eye have been prevented from entering the Minneapolis Lakes 56 times since the start of the MPRB program, but we can’t know if we removed plants that may have had very small ZM on them or drained water that contained zebra mussel veligers. The MPRB inspection program is not just about zebra mussels; there are many AIS that have potential to impact our lakes.

What impacts will this have on AIS inspections at Lake Harriet?
There will be no changes to inspections at Lake Harriet because:

Whether or not a lake is listed as infested, Minnesota law requires boaters and anglers to:

  • Clean watercraft of aquatic plants and prohibited invasive species,
  • Drain all water by removing drain plugs and keeping them out during transport, and
  • Dispose of unwanted bait in the trash.

It is important to remember that zebra mussels are not the only invasive species that we are trying to stop from spreading.