The U.S. Coast Guard is giving up its plan to set up 34 live-fire zones in the Great Lakes so its crews could practise shooting machine-guns.

Each of the zones on lakes Superior, Michigan, Huron, Erie and Ontario would have been closed to private vessels for four-hour spans about four to eight times a year. Exercises would have taken place in each zone two or three times a year.

Crews would fire at floating targets towed by cutters, rescue boats and other vessels. The weapons can shoot up to 600 rounds a minute.

During several public hearings in the region, coast guard officials said the training exercises were vital to its homeland security and law enforcement missions.

However, legislators, mayors, business leaders and environmentalists on both the Canadian and U.S. sides of the Great Lakes criticized the proposed gunnery ranges as unsafe and disruptive. Others said the lead bullets left behind would harm plants and animals in the lakes.

"I intend to reconsider the number, frequency of use, and location of water training areas as well as other concerns raised by the public," Rear Admiral John Crowley said in a statement issued from the coast guard's Great Lakes headquarters in Cleveland, Ohio.

"I am also committed to pursuing environmentally friendly alternatives to the lead ammunition we currently use," he added.

with files from the Associated Press