Officials say an aquatic invasive species may be establishing in a popular northwest Iowa chain of lakes.
The state Department of Natural Resources says three additional juvenile zebra mussels were found in December attached to docks and boat hoists removed from East Okoboji Lake.
The agency is monitoring the Iowa Great Lakes after finding a single zebra mussel in Upper Gar Lake in September.
A DNR spokesman says it's too early to tell if the zebra mussels are reproducing in the lakes. Officials also say it's unclear what an infestation would do to the area.
Zebra mussels are filter feeders. They directly compete with native species, including mussels and small fish.
The agency says there is no treatment to eradicate or control the mussels once they infest a lake.