http://sacramento.cbslocal.com/2011/04/11/two-die-while-scuba-diving-in-jamestown-mine/

A scuba diving trip to an old mine in Tuolumne County led to the deaths of two men over the weekend, authorities said.
The Tuolumne County Sheriff’s Department said four friends went diving at the closed mining pit off Harvard Mine Road on Saturday afternoon. One of the men, identified as 37-year-old Jamie Pollard, a Stockton resident, suddenly started struggling underwater for unknown reasons.
One of the other divers, 41-year-old Cameron Wheeler, helped bring Pollard to the surface and called for help from authorities. Pollard appeared to be fine, but was pronounced dead sometime later after being rushed to the hospital.
Wheeler went back into the water to search for another diver, 34-year-old Lodi resident Dale Allen Dedic, who was last seen at a depth of 130 feet. When Dedic was not found at depth or at the surface, Wheeler called authorities.
The Army Corps of Engineers used special equipment Monday to search for the missing diver and found Dedic’s body at a depth of about 135 feet. Officials are still trying to recover the body.
The causes of the victims’ deaths have not been determined.
The Harvard pit was one of several sites in the area that yielded more than 660,000 ounces of gold during mining efforts between 1986 and 1994. After the mine closed, water runoff rapidly filled the pit.
A brother of one of the victims said the four men were experienced divers who had permission from the property owner to practice in the clear, still waters.
A report from the U.S. Geological Survey in the late 1990s showed that an unsafe amount of arsenic and other toxic chemicals has been found in the water.