Spiny waterflea Lake Mille Lacs

Spiny Water Flea Threat

in Central Minnesota

Important Points:

1. This invasion is the first outside of Lake Superior and the US-Canadian border waters.

2. The waterfleas compete with small fish for food. This may affect the availability of smaller fish as a food source for larger fish.

3.  The waterfleas collect in sticky masses and attach themselves to fishing lines, anchor lines and downrigger cables. They may be spread when this equipment is used in other lakes.

Crosslake is only 40 miles from Garrison (on Lake Mille Lacs).


Spiny waterfleas discovered in Lake Mille Lacs

(Released September 22, 2009 by Minnesota DNR)


The Minnesota Department of Natural Resources (DNR) Aitkin

Area Fisheries staff discovered spiny waterfleas in Lake Mille Lacs

last week. The discovery of this invasive species is the first

outside of Lake Superior and the U.S.-Canadian border waters,

such as Lake of the Woods, Rainy Lake and Namakan Lake.

Spiny waterflea impacts to lake ecosystems are largely unknown.

The waterfleas compete with small fish for food called zooplankton.

While larger fish eat them, tiny fish may not be able to consume

this invader. In certain types of lakes, they can change the species

and numbers of zooplankton, which may harm those lake ecosystems.

However the water fleas can collect in masses, sticking to fishing lines,

downrigger   cables, and anchor lines. The masses can resemble

gelatin or cotton batting with tiny black spots, which are the creatures’

eyes or eggs. Individual animals are difficult to distinguish without

magnification because they are only 1/4 to 5/8 inch long.

The spiny waterfleas in Lake Mille Lacs were first observed collecting

on fishing lines in the water. The find was later confirmed from water

samples collected by the DNR.

“Spiny waterfleas can spread when boats, fishing or bait harvesting

gear become contaminated with egg-laden females or when water

from the infested lakes and rivers is transported,” said Rich Rezanka,

DNR invasive species specialist. “Although the waterfleas may die

between fishing trips, they might be carrying resting eggs that can

begin a new infestation.”

Spiny waterfleas are zooplankton – microscopic crustacean animals

like the Daphnia in lakes. They have a long tail spine with up to three

pairs of barbs sticking out of it. As a predator, they eat other

zooplankton, and they often can become abundant in late summer and fall.

Anglers are often the first to discover spiny waterfleas because they

become tangled to fishing gear. The waterfleas can be a nuisance to

anglers, collecting in gobs on fishing lines.

In response to this new infestation, the DNR will:

Update the signs at water accesses on Mille Las to indicate the presence of the waterfleas.

Continue watercraft inspections and enforcement efforts around the lake that were increased in 2009 due to zebra mussels.

Provide area business with information on spiny waterfleas.

Regulations prohibiting the transport of water and requiring draining of livewells, bait containers, and bilges are already in effect at the lake due to its zebra mussel infested water designation.

Monitor spiny waterflea populations as part of an assessment of impacts to the lake.

Before leaving the water access, boaters and anglers should:

  • Remove aquatic plants and animals, including gelatinous or cotton-batting-like material from fishing lines, downrigger cables, anchor ropes or waterfowling decoy cords.
  • Drain water from livewells, bait containers, and bilges by removing the drain plugs (Those who want to keep live bait must replace lake or river water with tap or spring water).

Boaters and anglers should also:

Dispose of unwanted live bait in the trash.

Spray the watercraft and gear with hot high pressure or hot tap water for several minutes before transporting to another water or;

Dry the watercraft and gear thoroughly for at least 24 hours and preferably five days before transporting to another waterway.
Experts believe spiny waterfleas originally arrived in the U.S. from Eurasia in the ballast water of cargo ships. They were first found in Lake Superior in 1987.