DECATUR, Ill. (AP) — Fishermen with a net are removing thousands of Asian carp from Lake Decatur dam in central Illinois.

The effort began Monday, days after the state was told that many fish were gathering there, The Herald and Review reported. The invasive species will be trucked to a company in Bushnell, Illinois, which will process them for fish meal and fish oil.

Kevin Irons of the Illinois Department of Natural Resources said some fish appear to be 20 to 30 pounds. The net is 30 feet deep.

The Sangamon River is impounded to form Lake Decatur in Decatur. A barrier prevents Asian carp from jumping into the lake.

In May, the Army Corps of Engineers approved a $778 million plan to block the carp from reaching the Great Lakes. The fish can cause serious damage by dominating native fish for food and space.

Asian carp were brought to the United States in the 1960s and 1970s to control algae, weed and parasite growth in aquatic farms. They escaped into the Mississippi River and have been spreading ever since, changing the ecology of bodies of water wherever they take root. Some species are also known for jumping high out of the water, which can cause injury to boaters and other recreational lake users.

The dam was turned off for a short time Monday morning in an effort to draw out as many of the fish as possible while fishermen sailed along the perimeter of rocks near the dam. They used a 30-foot deep seine net, which is designed to catch fish like Asian carp. Irons said the fishermen try not to remove native species along with the invasive carp.

Irons said the commercial fishermen have been sent out to the Illinois River recently to use the exact same deployment process for the carp.

There are four species of carp that, together, are commonly called “Asian carp,” according to the National Park Service. They are bighead carp, black carp, grass carp and silver carp. Irons said the fish spotted in Lake Decatur so far appear to be silver carp, which feed almost continuously on plankton and can leap as high as 10 feet out of the water, and black carp, which eat mussels and snails and have teeth similar to human molars.