New research suggests many of the beaches around Bras d'Or Lake in Cape Breton will be underwater in 50 years.

John Shaw, a marine geologist with the Geological Survey of Canada, has wrapped up a detailed underwater mapping project on the inland sea in the centre of the island.

He predicts water levels will rise by 76 centimetres by the end of the century, partially due to climate change.

"It's not just because the ocean is rising up, because of melting glaciers and expansion of the ocean water because of rising temperatures," said Shaw, "but also because the land in Atlantic Canada is subsiding very rapidly."

He said that's a long-term effect of the last ice age, and it makes the problem much worse.

"By 2100 I think the situation could be pretty catastrophic on the shorelines, but certainly by the middle of the century a lot of the beaches are going to be gone."

Shaw said the four-year project was launched because researchers knew very little about the bottom of the lake.

About 20,000 years ago, a series of lakes were carved out by glaciers that covered the area. Then about 6,000 years ago the ocean came flooding in and turned them into an arm of the sea.

Using sonar systems, Shaw could see the old shoreline, which is now 25 metres below the modern sea level.

He expects the new maps will be useful to other scientists and researchers studying the area.