NEW YORK (

TheStreet

) -- The U.S. Environmental Protection Agency has begun to draw a link between fracking and water pollution.

The EPA began investigating water in parts of Wyoming three years ago and said in a draft report on Thursday that it's found the ground water that had compounds in it related to natural gas production.

"The explanation best fitting the data for the deep monitoring wells is that constituents associated with hydraulic fracturing have been released into the WindRiver drinking water aquifer at depths above the current production zone," the draft report said.

Shares of some fracking companies fell Thursday.

Chesapeake Energy

(CHK) - Get Report

shares dropped 5.09% to $24.23 and

Devon Energy

(DVN) - Get Report

fell 4.17% to $63.73.

Water treatment companies have been looking at

treating water related to fracking as a potential new revenue stream.

Cameron International

(CAM)

, which has cornered more than half oilfield water treatment market, saw its stock slump more than 3% on Thursday.