Warm weather/water affects fishing
Elevated water temperature results in stratification of the water column. The water column is what you would picture if you extended a tube from surface to bottom and analyze the conditions in each "tier."
This would be comparable to what you'd see if you took a soil sample. There would be layers of black dirt, sand, rock, all of the elements in sections that show the timeline for our land structure, over decades and centuries.
Water acts a bit differently, since the changes, at least where there is water versus soil, are dramatic over months, not years.
When water warms, the water column, which stretches from surface to bottom, stratifies into three layers.
The uppermost section contains ample amounts of dissolved oxygen, yet the temperature is the warmest. Species like smallmouth bass, walleye and northern pike prefer cooler climates. The bottom-most layer has very cool water, sometimes 20-degrees lower than the upper layer of water. This would be suitable for those species, yet the oxygen levels declines the deeper you travel. Smallmouth bass, walleye and northern pike cannot survive for extended periods of time in the bottom section, especially if you're trying to target fish on the bottom in more than about 35 feet of water.
The middle section is called the "thermocline" and predators enjoy circulating in that center band of cool water that has good oxygen levels. However, catching fish in this section can be difficult and at times frustrating.
Each of these cool water species will eventually travel toward shallow water to feed. Even if their food source, such as cisco and tullibee are available in deep water. Cornering a meal up against a point, hump or weedline is much easier versus trying to latch onto a smaller fish that can escape vertically or horizontally without obstacles. Imagine humans playing a game of tag in a gymnasium versus the open fields of North Dakota. Deep water fishing creates difficulty for predators to "tag" their prey.
Currently, the walleye have been harder to catch because of the water stratification. Getting a bait to dive into the thermocline where the greatest majority of the walleye are suited takes precision. Jets, dipsy divers, leadcore line, deep diving crankbaits, down-riggers and confidence that you're targeting the correct depth are all variables.
Smallmouth bass, the hardest fighting fish pound-for-pound in our lakes, are active swimmers throughout the day. Fish can be found in shallow water environments, mid-depth levels and deep water depending on both their mood and forage availability. Smallmouth typically attempt to eat either minnows or crayfish, though aquatic bugs are a staple in their diet during the early portion of the fishing season.
Those deep-dwelling fish will come shallower to feed, especially in the low-light hours such as sunrise and sunset. So early morning and late evening provide a good opportunity to fish the 12-20 foot range. Yet during the mid-day hours, go deep, or go home.