A lake has a pH of 3.5. Is it acidic or basic? Would fish be healthy in this lake?
The lake is acidic. This is not normal, not to this degree anyway. The fish would likely not be healthy.
The pH scale goes from 1 to 14 with 1 being really acidic and 14 being very basic.
Each step up in the scale is equivalent to 10 times the concentration of the previous step.
Neutral water has a ph of 7 but generally a pH of 6-8 is normal. the recommended pH for fish is between 6.0 and 9.0.
So a pH of 3.5 is many times more acidic than normal. To use an example this would be like the fish swimming in vinegar so definitely not good.
But then, of course, it would depend on the fish. They might have developed to live in this lake and so would be fine with it.