Answer: The Allele frequencies in the fish population will become more similar over time.
Explanation: The Allele frequency also known as the gene frequency, is the relative frequency of an allele (which is a variant of a gene) at a particular section in a population, normally expressed as a fraction or percentage.
To be more precise , it is the fraction of all chromosomes in the population that carry that gene.
If during a flood event a permanent stream forms between two lakes allowing fishes to move back and forth, it would cause the allele frequencies in the fish population to become more similar.