The Coast Guard learned the dredge, called the Arthur J, was sinking about 4:35 a.m. today as it was headed toward the St. Clair River. The dredge and a 38-foot tug,  sunk in 22 feet of water in Lake Huron about 2 miles off of Lakeport. The captain on board the 110-foot commercial dredge  estimates the vessel carried 1,500 gallons of diesel fuel at the time of its sinking this morning.  MCM Marine Inc. Sault Ste. Marie, owner of the dredge, has hired Michigan Pollution Control to make a response plan to clean up the diesel fuel spill. The U.S. Coast Guard is monitoring the clean-up efforts and is assessing the rate at which oil is leaking out of the dredge.  The Coast Guard in Port Huron responded to the scene with a 25-foot response boat.  It is reported there is a sheen on the water around the sinking site. Members of the Coast Guard are investigating that issue.