A lake has a low pH. Is it acidic or basic? Would fish be healthy in this lake?
A low pH means that the lake is acidic.
Here is a diagram of the pH scale:
Fishes are unable to survive in acidic conditions as the natural pH of lakes should be 6 or 7. Here is an excerpt on what happens when the pH decreases
As the pH approaches 5, non-desirable species of plankton and mosses may begin to invade, and populations of fish such as smallmouth bass disappear.
Below a pH of 5, fish populations begin to disappear, the bottom is covered with undecayed material, and mosses may dominate nearshore areas.
Below a pH of 4.5, the water is essentially devoid of fish.