which is the following contributed most to fish population dying during the 1970?1. salt 2. toxic waste 3. predators 4. mercury 5. iodine

Answer 1

In Australia, 14 percent of fish kills were due to low levels of O2, 8 percent due to pesticide/toxic waste, and the other causes lessor.

http://www.fisheries.nsw.gov.au/__data/assets/pdf_file/0017/5057/nsw-fishkill.pdf

In the early 1970's, the James river had a major long term fish kill due to toxic waste, this caused a lot of public attention on clean water, and focusing on point source contimanations.

Answer 2

Toxic waste