The Texas Parks and Wildlife Department believes low oxygen levels in the water are killing the fish, and hotter days ahead may mean more of the same.
Large amounts of fish -- primarily shad, but also flounder and even stingrays -- began washing up on shore on Saturday. Most of them were on west Galveston's Seawall.
And they stink.
"Oh, my gosh. Oh, my gosh," beachgoer Terri Knop said. "I can't describe how many fish are around here"
But for David Lopez and his family, who are breaking in their new beach house, the smell won't spoil their fun.
"My daughter, she's six years old. She said, 'what's that rotten smell?' And I said, 'I don't know,'" Lopez said. "Actually, once you've been here a while, you just get numb to the smell so it's not that terrible."
According to Texas Parks and Wildlife officials, the shad fish are washing up because of red tide in the Galveston area caused by a high concentration of microscopic algae.
Officials say you should not swim in an area where there are a lot of dead fish because the fish are decaying, which means higher levels of bacteria.
"It's hard to even get past without stepping on one," Callum Glover, 8, said.
Health experts say the concentration isn't enough to pose serious dangers to swimmers and surfers. Still, crews are feverishly working to collect and dispose of the dead fish so beachgoers aren't tip-toeing around their last days of summer.
Crews will continue to work until all 32 miles of Galveston beaches are cleared.
The problem is that more fish are washing in, albeit in smaller numbers.