We have three fishable reservoirs up here in South Park (Spinney, Eleven Mile, and Tarryall – Antero is closed). We usually start float fishing Spinney as soon as the gates open, mid- to late-April. We either put the Bayliner in or row around in the dory. We don’t much use our inflatable boats yet because it is still pretty cold until about June. As it is, Spring turn-over usually happens right after we start fishing.
What exactly is turn-over and how long will it last?
Over the course of seasonal changes in a year, lakes develop a stratification in temperature. Think layers like oil and vinegar in a bottle. When you have wind, the layering of water gets mixed up a bit more so there is not such a contrast of temperatures during the summer. However, when cold air begins to arrive for longer periods of time (like in the fall) and there is less sun light (moving into winter) the stratification is enhanced. Eventually in the fall, the surface water will become more cool and dense, than the lower water and that upper layer will flip with the lower layer of warmer, less dense water.
Now, you have just shaken up the bottle of oil and vinegar. What does that liquid look like? It is murky because all the dead stuff that was settled to the bottom of the lake has been shaken up as well. Fishing is off because cloudy water has the same effect on trout as a dusty day has on humans – think allergies – yuck.
In the spring right after the ice melts on a lake, turn over happens again due to the opposite conditions: The water at the bottom of the lake has stagnated and dead material that has settled on the lake bottom has been decaying and producing methane gas. Stratification occurs during the winter months because ice has prevented wind from mixing the water and you now have layers of less dense water with methane gas on the bottom and denser water on top. When the ice melts, the sun and wind re-oxygenate the surface water and its density increases. Then – WOOOSH! The layers flip. Same effect: cloudy water puts the fish down.
How long does it take to recover from a flip? That depends on how stable the surface of the water is – how big the lake is, how much surface area is available, if the weather is windy etc. At Spinney Reservoir the last couple of years, the spring turn over affect has put fishing off for about 2 weeks. Then, once the fish recover, the fishing is consistent and easy at Spinney (as long as you play the “depth-versus-hatch” game with the trout.)