MILFORD, Iowa (AP) — Officials say they think a nearly $1-million electronic fish barrier has succeeded in stopping invasive Asian carp from the Iowa Great Lakes. The Sioux City Journal reports the fish first swam into the lakes during flooding in 2011. They had previously been kept out by dams on the Little Sioux River in Harrison County and near Linn Grove.

The Asian carp species are thought to be a major threat to native aquatic species throughout the Midwest. One species, the silver carp, poses a safety hazard because they leap from the water when startled.

The 21-foot-long fish barrier was built in 2012, and officials believe it’s working. There have been few reports of Asian carp being netted or sighted