In the end, Billy went to check the lake by himself when on a day off, even if it was fun, no one could swim every day. Also, the girls were reaching the fifth month of pregnancy, so they were getting tired more easily.
Without wasting time, Billy dived into the lake, and it didn't take long for him to realize that the inclination of the bottom was very similar to that of a crater. Some time had passed since that thing had been created, so there were some plants blocking the view, but even so, Billy could confirm that.