Scuba-divers reached 40th depth under water but didn't see the bottom. Many passages are extended to some hundredes metres in clay and gypsum. It could seem that water in different collapse sinkholes must be the same. But in reality all collapse sinkholes are very particular. In some places the water containing sulfuric hydrogen is formed in lower layers of water by bacterial sulfate reducing process.
Sulfuric hydrogen is oxidated and water transforms to sulfuric acid.
It was one case when scuba-divers lowered rubber boat in sinkhole and while they has been going down the boat was soluted. Many strange creatures live in underground sea. Some species of relic crayfishes were found by zoologist of Moscow University - Levushkin. In 1981 in karst collapse sinkhole Maltsev found new species of blind fish. This fish was described by Parin from Evolutionary Morphology and Ecology of Animals Institute as Starostin loach or Kougitang blind loach.