Onum Lake has 25 more trout than Boast Pool.  There are 75 fish in Boast Pool. Riddle Pond has half as many fish as Onum Lake. What is the average number of fish in all three bodies of water? Let's think first. Chain of thought:
Onum lake has 25 trout + 75 = 100 fish. Riddle Pond has 1 / 2 * 100 fish in Onum lake = 50 fish. Combined the three bodies of water have 100 fish + 50 fish + 75 fish = 225 fish. The average number of fish in the bodies of water is 225 fish / 3 = 75 fish.
Therefore, the answer is 75.