Answer:
1. Genetic drift, which is a random change in allele frequencies in a population over time, could lead to changes in the allele frequencies of the population of trout, causing them to not be at Hardy-Weinberg Equilibrium.
2. There could be a non-random mating system in place, such as assortative mating, that also affects allele frequencies and leads to the population not being at Hardy-Weinberg Equilibrium.