SHOREWOOD (AP) -- Officials say they're encouraged with initial results from an effort to kill zebra mussels infesting Christmas Lake west of Minneapolis.

The Minnehaha Creek Watershed District used the bacteria-based pesticide Zequanox to treat the area around the public boat access on the lake earlier this month.

Staffers said Thursday that it appears to have killed all the zebra mussels in the treatment area.

Divers found and removed around 25 live zebra mussels outside that area last Friday.

Officials now plan to expand the containment zone, and they're considering alternatives to Zequanox, which isn't as effective in colder water.

Christmas Lake was selected for the test because the infestation was detected early.

It marked the first use in the nation of Zequanox outside of small experiments or power plant water pipes.