A joint U.S. and Soviet research team exploring the bottom of the world's deepest and oldest lake announced last week that it had discovered hot vents and an associated community of sponges, bacteria, worms and fish.

The deep vent community, in the Soviet Union's Lake Baikal, is the first to be found in fresh water and may represent a snapshot of a lake in the act of becoming an ocean. Scientists say the unique community is a treasure for researchers studying evolution. Most lakes are only thousands of years old. Lake Baikal in Soviet Siberia may be 25 million years old.

The disovery was announced by the National Geographic Society, which along with the Soviet Academy of Sciences supported the expedition.

The vent community, photographed from a Soviet submarine, lies at a depth of 1,350 feet. The crescent-shaped lake lies in a rift valley that is pulling apart, and may someday split the continent open and turn the lake into an ocean.

The Baikal vents cover an area about the size of two football fields, where water warmed deep in the Earth percolates upward and nourishes a community of shimmering white bacteria and mushroom-shaped sponges. The community will be compared to others discovered at hot vents located along mid-ocean ridges, such as those discovered near the Galapagos Islands.