Thousands of Threadfin Shad fish bellied up over the weekend at Santa Fe Lake. Investigators with the Florida Fish and Wildlife Commission believe it's when algae in the water can no longer get energy from the sun, they use the oxygen in the water. Most species usually go deeper into the water where there is more oxygen, but the shad prefer to stay on the surface. It could take up to three to four days before the fish decompose. Residents hope that will happen before Labor day weekend.