For many decades, flood irrigation was the norm so all the excess runoff flowed into the Salton Sea. When sprinkler irrigation became the norm, much less runoff flowed to the sea and the increase of salt/brine as evaporation was greater than refill. The man made chemicals started flowing into the sea ever since WW2.Yes, it has had water since the first few floodings in the early 1900's, but it is my understanding that it had a significantly higher water level
(Fresh water that allowedan aquaculture to form) and the original die off was from salt and mineralization from the old sea floor and run off from the mountains. The chemicals came later.....
Back in 2019, my wife and I drove around the Salton Sea to look at all the various ruins.