British diver Martin Robson has been placed in intensive care after making a record 209-meter dive in Blue Lake in Russia’s North Caucasus on Thursday, the lake's diving center said.

At 258 meters in depth, Blue Lake is considered to be the third largest lake with only underwater tributaries in the world and the second largest in Europe. An international project to explore the depths of the lake is currently underway.

“The record immersion continued for about nine hours. Robson successfully resurfaced from a depth of 209 meters but later became ill and was taken to the republic’s hospital in Nalchik,” a spokesman for the diving center said.

One member of Robson’s support team, Russian diver Andrei Rodionov, 39, died on January 13 during one of the first dives.

Researchers believe there is a very deep cave system in the lake.

One of the project objectives is to locate, penetrate and explore this cave system, and to prove that Blue Lake is the deepest karst spring in the world.