Can a moderately fertile (mesotrophic) lake hold trout?
Only if it is deep enough to win the summer race. A trout needs cold water and oxygen in the same place — roughly 6–7 mg/L of oxygen, in water below about 20 °C (68 °F). In a stratified lake that place is the cold layer under the thermocline, which is sealed off from the air all summer and only loses oxygen as sinking organic matter decays. The more fertile the lake, the faster that bank account drains. A truly infertile lake stays habitable year-round; a mesotrophic lake is the borderline case — a deep basin may carry rainbows or lake trout through to fall turnover, while a shallower one of the same fertility runs out in late summer. Ask about depth and late-summer oxygen before you ask about stocking.
The full story
This answer is one piece of a longer lesson — setups, diagrams and the reasoning behind it.
More questions about Territory & aggression
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