There have been more dead fish floating on the surface of some lakes recently. This means oxygen levels continue to drop in the deepest portion of many lakes in the Bemidji area.

Cold water species such as tullibees, whitefish and suckers are most affected by the combination of warm water and low oxygen levels during the summer.

They try to stay in the coldest parts of the lakes where oxygen levels are high enough to support them. They need to be able to find enough food to eat to keep them alive in what can be a very narrow portion of the water column.

Other species such as walleyes and muskies can also struggle in the warm water when they get caught and released. They need to be able to recover fast enough to resume their normal feeding patterns or there can be delayed mortality from getting caught.

This is an annual issue during the hottest part of the summer. The extent of the die-off varies from year to year. The long-term warming trends exacerbate the problem.

The historic range of tullibees and whitefish in Minnesota is changing one lake at a time. Experts have serious concerns for the long term viability of cold water species towards the southern end of their range, which includes the Bemidji area.

Tullibees and whitefish spawn in the fall, so their young of the year are just the right size in the spring for post spawn walleyes, bass, northern pike and even muskies, which all use them as a key forage species.

Suckers, shiner minnows and eelpout are also cold water species that can negatively affected by elevated water temperatures.

It is not only how warm the water temperatures get during the summer, but how many days the water temperatures remain elevated. The longer the lakes stay near their peak temperatures, the more cold water species will be affected.

Most fish in the lakes are in less than 40 feet of water, with only a few lakes capable of holding fish deeper than that in the summer.

Cass Lake and Walker Bay of Leech Lake would be two examples of lakes where fish can be deeper than 40 feet right now.

The general direction of most fish is toward shallower water, with the deep edge of the weed beds, the tops of structures and rock piles at various depths are all examples of areas currently holding fish.

Vegetation growth in the lakes is about as thick as it’s going to get for the year. Many aquatic plants still have to be pollinated in the air, so plants like cabbage weeds and coontail need to reach the surface of the lakes to be pollinated and begin to form their seeds.

The mature plants pull back slightly from the surface of the water from the weight of the growing seeds. Once the seeds are mature and the plants start stop growing, wave action breaks off the heavy tops of the plants and spreads the seeds around the lake.

Invasive species like Euroasian Milfoil will also form seeds, but they have an evolutionary advantage over native vegetation because they spread by runners underground and by fragmentation. Any portion of the plant with some stem is capable of starting a new plant when it gets broken off and transported by the waves or by people’s boats to another location.

We are living in a new age on the lakes, with dramatic changes to the ecosystem, which makes it hard to predict what the future will look like.

Change is one of the few constants. Our grandparents’ lakes will not be our children’s lakes. The legacy we are passing on to the next generations should matter to everyone and this includes the entire environment, not just the lakes.

The life experience of most of us has been trying to improve and protect the environment and try to make things better than they were before. We have been backtracking the last few years, which is not good for anyone.

Paul A. Nelson runs the Bemidji Area Lakes Guide Service. Guided trips can be booked by calling or texting 218-760-7751 or by email at panelsonbemidji@gmail.com.