The Farmington River Water Quality Station is up and running and monitoring water temperature and dissolved oxygen. Additional sensors will soon be installed which will monitor conductivity and pH. Alarm triggers for high water temp and low oxygen have been programmed and are functioning. Access to the station is by the link below....
https://www.licor.cloud/dashboards/eda68687-2b7c-4521-bfa3-117e94dc04c9/true
Below is some information describing water temp and dissolved oxygen and the effects on various trout species....
Trout are cold water fish with narrow tolerances for both temperature and dissolved oxygen (DO). Kill-offs occur when both factors cross critical thresholds simultaneously, and their interaction is nonlinear — meaning warmer water + lower DO is much more lethal than either alone.
Dissolved oxygen (DO) increases during the warmest part of the day primarily due to photosynthesis.
• Sunlight fuels photosynthesis in aquatic plants and algae.
• This process produces oxygen, which is released into the water.
• The most intense photosynthesis happens in the afternoon, when sunlight is strongest — even if water temps are rising.
• Despite warm water holding less oxygen, the rate of oxygen production from photosynthesis can outpace oxygen loss, causing DO to spike.
So, even though warmer water holds less oxygen, daylight-driven photosynthesis adds more oxygen than is lost — until the sun goes down.
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The Balance: Temperature vs. DO
• Colder water holds more DO:
• At 50°F (10°C) → ~11 mg/L DO is possible
• At 75°F (24°C) → max DO drops to ~8 mg/L
• But it’s not just capacity — trout need more oxygen as water warms:
• Metabolic rate increases, requiring more oxygen, even as less is available.
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How Kill-Offs Happen:
1. Hot weather → water heats up (esp. in shallows & slower flows)
2. Algae & aquatic plants respire at night, drawing DO down
3. DO dips below 5 mg/L, especially near dawn
4. Water is ≥70°F → trout metabolism spikes, oxygen demand surges
5. Fish enter oxygen debt → stress → suffocation → death
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Key Metrics for Monitoring:
• 68°F+ water temps for multiple days → dangerous
• 70°F–72°F water + DO below 5 mg/L → high mortality risk
• 75°F+ for several hours → lethal, even if DO is decent
• DO below 4 mg/L for more than an hour → often fatal regardless of temp
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Sensitive Species:
• Brook trout: Most sensitive; start stressing around 65°F, die above 70°F
• Brown trout: Slightly more tolerant, but long exposure to 70°F+ is still deadly
• Rainbow trout: Slightly more tolerant than browns, but still vulnerable
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Best Practices:
• Stop fishing when:
• Water temps hit 68–70°F
• Flows are low and warming quickly
• Fish early mornings when temps & DO are highest
• Use thermometers & DO meters if you guide or monitor river health