Why do trout lakes need to be deep or spring-fed?
Because a trout needs cold water and oxygen in the same place at the same time, and summer tries to separate them. A stratified lake in July offers warm oxygen-rich water on top and cold water below — but that cold bottom layer is sealed off from the atmosphere, so its oxygen only gets consumed, never replenished, until fall turnover. Only deep, relatively infertile lakes keep enough oxygen banked in the cold layer to carry trout through; in fertile green lakes, decomposition burns the deep oxygen out by midsummer. Springs solve the problem locally, injecting cold oxygenated water year-round — the reason tiny spring ponds can hold brook trout that a much larger warm lake cannot.
The full story
This answer is one piece of a longer lesson — setups, diagrams and the reasoning behind it.
More questions about Breathing & oxygen
Same topic, other species
- Why are summer crappie pinned to one exact depth band? — Crappie
- How does the thermocline affect where largemouth hold in summer? — Largemouth Bass
- Why do muskie suspend over open basins in summer? — Muskellunge (Muskie)
- Is there enough oxygen in the deep basin under the ice? — Yellow Perch
- Why can't big pike just go deep in summer where the water is cold? — Northern Pike
- Does a summer smallmouth have to move deep? — Smallmouth Bass
- How does the thermocline decide where summer walleye live? — Walleye