CARIBOO OUTDOORS: Climate Change and lake health

CARIBOO OUTDOORS: Climate Change and lake health

Published 5:00 pm Tuesday, January 6, 2026

I couldn’t help but notice how low most of our local lakes were all last year. So I got to thinking (I know my friends are chuckling at the thought of me doing that), how might low water conditions affect the health of a lake and the fisheries in them?

I did a little research and found a scientific paper by Ken Ashley, Ph.D., R.P. Bio. titled “Predicted Impacts of Climate Change on BC Lakes” dated Jan. 25, 2024. I know that the term climate change gets bandied about, and I’m sure everyone has an opinion about whether it is real or contrived, but as evidence mounts it is certainly being taken seriously by members of the scientific community.

While the paper speaks as well to potential hydroelectric issues, I will focus more on how climate change could impact our local lakes. I certainly learned some new terminology to describe lake turnovers, a subject I wrote about in earlier columns.

Firstly, dimictic is where a lake turns over twice a year, which we experience locally for the most part in our smaller lakes; monomictic, where a lake only turns over once a year, and mixes completely; and meromictic describes a lake which has layers of water that do not intermix. The latter two are more relevant to deeper lakes.

Of concern to us on the plateau here, the smaller lakes that normally are dimictic may eventually become meromictic, where the water levels don’t mix vertically (eg. epilimnion, thermocline, and hypolimnion). If readers recall, once a lake stratifies, the upper layer or epilimnion of water is warm, the middle layer, called the thermocline, is a mixture of the warmer water above and the cooler, denser water found in the bottom layer or hypolimnion.

If the water fails to stratify in a given lake, then it may experience temperatures that could exceed the 25 C that is the maximum trout can live in. Insufficient oxygen could also pose issues in these lakes, as well, leading to both summer and winter kills.

Another issue of concern is that as the lakes evaporate, concentrations of dissolved minerals in the water will increase, resulting in the alkalinity or converesely, the acidity increasing. For reference, I have attached a table showing the scale of acidity to alkalinity. It ranges from a pH scale of 1 (very acidic) to 14 (very alkaline), with a neutral pH being 7.0. It is worth noting that fish cannot tolerate an acidic level of 4.0 or below, with ideal preferences around 6.5.

On the opposite end of the spectrum, most fish cannot do well in pH levels above 9.0. While I did not reference any of the pH levels in most of our lakes, I did find out that Green Lake typically has a pH level between 8.5 and 9.5. What this means is that as evaporation occurs, the pH level will rise.

Kokanee do best in pH range between 6.5 to 8.5, while rainbow trout thrive in a slightly narrower range of 7.0 to 8.0. I will let the reader draw their own conclusions on how this will impact the fisheries.

For readers who may be interested, I have generally categorized acidic lakes as being a bit brackish, tannic stained with lily pads and muddy bottom upon observation, while alkaline lakes (above 7.0 pH) are generally a lot clearer with green coloured (marl) bottoms. This is my rule of thumb for making a quick determination of the rough pH level of a lake.

While changes affecting most of our lakes will occur over time, with the shallower, nutrient-rich, eutrophic lakes succumbing first, it is important to note that Green Lake is closing in on a pH precipice if evaporation from the lake continues. We have already seen a summer kill on Earle Lake as well.