Spiny waterfleas – tiny zooplankton with a big impact

April 18, 2021

Who really cares about a predatory zooplankton that can barely be seen with the naked eye?

Fishermen might care when gelatinous blobs stick to their fishing poles and prevent them from landing a fish or their catch is lacking.


Spiny waterfleas are a zooplankton (crustaceans, not insects), that live in open water.

Adults are about the size of a grain of rice and are opaque in color. They have a single long tail with one to four spines and have one large, distinctive black eyespot.

Most abundant in late summer and autumn, they compete with native fish for zooplankton.

They are an aquatic invasive species first identified in the U.S. in 1982 on Lake Ontario. Authorities said they were likely introduced through discharge of contaminated cargo ship ballast water. By 1987, they had spread to Lake Superior.

Spiny waterfleas are now infecting 66 water bodies in Minnesota, according to Meg Duhr, research outreach specialist with the Minnesota Aquatic Invasive Species Research Center (MAISRC).

In a study by the MAISRC, results revealed that spiny waterfleas were present in Mille Lacs Lake and Lake Kabetogama before they were first detected in the water column using plankton tows (2009 in Mille Lacs and 2007 in Kabetogama). This pest could have been present in both lakes during the 1970s and possibly as early as the 1930s.


Research has shown that spiny waterfleas affect walleye growth and survival. They are eating the food sources for fish. Only young perch have been able to adapt to the food changes wrought by the invaders, for now.

According to MAISRC research, recreational boaters and anglers are the main sources of inland spread. Studies showed trolled angling lines, anchors, downriggers, live wells and bait buckets collected the most spiny waterfleas.

“This is why replacing bait water is so important,” said Steve Hughes, district manager of the Aitkin County Soil and Water Conservation District. “For the last few years, area bait shops have been providing extra bags of clean water to people buying bait.”

Hughes said draining all water from boats and other water-related equipment is crucial. Spiny waterfleas can be removed by cleaning the equipment with a shop vacuum or towel. Live wells and bait buckets should be drained and dried.

“Clean, drain and dry is of utmost importance with this species,” said Duhr. “In dry summertime conditions, eggs and adults will perish if left dry for six hours. Drying equipment for 24 hours is the best way to ensure that you are not transporting viable spiny waterfleas or their eggs.”

More information about aquatic invasive species may be obtained by visiting StopSpiny.org or mndnr.gov or by calling Hughes at 218-927-7284 or emailing [email protected].

As always, stopping the spread of invasive species to other lakes and rivers protects habitat for native species such as sunfish and crappies. Overall lake and river health is better without invasive species. Healthy lakes and rivers benefit fish, wildlife and people. Remember, “Clean, Drain, Dry and Dispose.”