Scientists diving for the first time to the bottom of Crater Lake said on Sunday they had found no evidence of the active thermal vents they think might be in the deepest lake in the United States.

Oceanographers from Oregon State University began making daily dives to the bottom of the 1,932-foot-deep lake late last week. The dives are part of a 10-year federally funded study aimed at determining why the cobalt-blue lake appears to be losing its clarity.The hunt for thermal vents was undertaken because the lake is surrounded by geothermal resources that environmentalists want to protect from development.

Scientists Jack Dymond and Robert Collier said they found no evidence yet that proved or disproved the theory there are still active thermal vents in the lake.