The answer to this is rolling friction
If B and b are the two alleles , B + b = 1 and B ^2 +2 Bb + b ^2 = 1.
If 16% of mice are homozygous black , B ^ 2 =0 .16, meaning B = 0 .4 and b = 1 - 0. 4 = 0 .6 .
Answer = Notice how you don't even need to know that 24% of the mice are heterozygous .
It causes eutrophication which means that the algae have too much nutrients and take over the pond, use the oxygen so there is not enough left for marine life, which die as a result.