Fall patterns are quickly developing on area lakes
The combination of a full moon, warm temperatures and calm winds made for near-perfect conditions for night fishing walleyes and muskies this past week.
The downside to the active night bite was the negative effect it had on the day bite for walleyes and muskies during the same time period.
Anglers were able to catch a few walleyes in the mornings and evenings during the full moon phase but fishing was tough during the rest of the day, especially when there were light winds with bright, sunny skies.
The first hard frost of the fall occurred this past week in the Bemidji area. This should help get the fall fishing patterns started and trigger what experts are calling a great chance for some spectacular fall colors later this month.
The frost should also help get rid of some of the bugs in the woods for hunters participating in the opening weekend of archery deer, grouse and small game hunting seasons.
Most lakes in the Bemidji area still had surface temperatures around 70 degrees earlier this week but the cold snap and significant winds later in the week dropped the water temperatures into the mid 60s in only a couple of days.
The later cold weather arrives in the fall, the faster the fall patterns usually develop. The fish can sense the length of days getting shorter and also react to other environmental factors in the lakes, so there is more to the equation than just water temperatures.
Food is a key element to both gamefish and panfish location in the fall. The cooling water temperatures hit the shallows hardest, which moves the baitfish into deeper water and makes them more vulnerable to predators.
Visibility in the lakes is constantly improving as the water in the lakes cools. Algae thrive when water temperatures are high but they die quickly when temperatures begin to drop in the fall.
There is usually a new layer of dead algae on the surface of the lakes each morning that can look as thick as pea soup after a really cold night. Algae break down quickly and the remains mix into the water and eventually settle to the bottom of the lake.
There continues to be some confusion among anglers about turn-over and the breaking down of the thermocline in the fall.
The thermocline is the thin layer of water that separates the warm surface water from the colder water on the bottom of deep lakes during the summer.
As the lakes cool in the fall, the warm water above the thermocline drops in temperature until it is similar to the temperature below the thermocline, which causes the thermocline to dissolve.
Turn-over in the deep lakes occurs much later than the breakdown of the thermocline. Water is most dense (or heaviest) when it gets around 40 degrees Fahrenheit.
When lakes turn-over in the fall the water near the surface becomes denser (and colder) than the water on the bottom. This causes the surface water to sink, which displaces the water on the bottom and makes it rise to the surface.
Turn-over is the mechanism deep lakes use to become fully re-oxygenated before winter. Turn-over occurs right before the lakes are ready to freeze and it signals the beginning of the cold-water period, which lasts until the lakes begin to warm again.
Shallow lakes don't have enough depth to have a thermocline because the entire water column gets rolled over periodically by high winds. Only the upper layer of the water column in deep lakes gets rolled over by the wind, while the water below the thermocline remains stagnant and does not mix with the water above the thermocline until turn-over occurs.
The cooler weather should help improve fishing for most species of fish this week. Fall patterns are usually fully developed by the time surface water temperatures drop below 60 degrees, which should happen soon if the current weather trend continues.
Paul A. Nelson runs the Bemidji Area Lakes Guide Service. He can be e-mailed at email@example.com.