Famous French speleologist and diver Frederic Swierczynski became the first man to ever reach the bottom of Red Lake in Imotski. On May 6th, Frederic Swierczynski hit the bottom at 245 meters, after a four-hour dive. Other than hitting the bottom of the lake, the goal was also to take samples of sediments and water at various depths. The team of scientist placed sixteen coops, fishing nets and trawl line at various depths in order to learn more about the organisms populating the lake. Frederic Swierczynski commented that he had seen a surprising number of shoals of small fish, a local species called gaovica.
Red Lake lies in a deep, roughly circular sinkhole. It is surrounded by almost vertical tall walls from three sides and slanted from the fourth side which collapsed during a destructive earthquake that hit Imotski back in 1942. Red lake is the deepest karst lake in Europe and one of the deepest in the world and it is almost impossible to approach it because of tall stone slopes around it. The depth of the sinkhole is around 500 meters, with a width of 450 meters. The diameter of the lake is approximately 200 meters and the depth is 290 meters. Beside the water lever of the lake, many small caves formed like the Čepitška Cave, with two entrances, one above and one under the water level. The cave is around 67 meters long. Red Lake is home to some organisms who live only in this lake and nowhere else in the world like the small, 12 cm long fish named Delminichthys adspersus. During dry springs, the fish can be seen in the springs in the area around the lake which is confirmation that the lake has underground connections with these springs.
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