An Introduction to Winter Lake Monitoring
The BCLSS office has been receiving many questions about monitoring lakes through the winter, so we’ve put together a short article outlining why winter lake monitoring can be valuable, along with some basic under-ice monitoring recommendations.
In a previous article we discussed the importance of monitoring dissolved oxygen and temperature in lakes which you can read here. The importance of these profiles can also extend into the winter, especially for relatively shallow, eutrophic lakes. When ice and snow cover a lake, it restricts or can effectively eliminate light penetration and thus photosynthesis. At the same time, decomposition within the lake uses up dissolved oxygen over the winter which can lead to the water becoming increasingly depleted of dissolved oxygen, or lead to total anoxia. Many fish species, especially salmonids, show signs of stress at dissolved oxygen concentrations less than 4 mg/L (Truelson, 1997). If the entire water column becomes depleted in dissolved oxygen, it can result in a large fish die off. When fish die under these conditions it is termed winterkill (Wetzel, 2001).
Understanding the potential impacts to fish populations is not the only reason monitoring under ice dissolved oxygen levels could be of interest. Additionally, low oxygen under ice may alter ecosystem balance and nutrient dynamics. For example, low dissolved oxygen levels can lead to internal nutrient loading (BCLSS, 2022). These are just some of the reasons that understanding dissolved oxygen levels under ice is important for many lakes throughout BC.
If you are interested in under ice lake monitoring to track dissolved oxygen levels over winter, here are our general recommendations. If you are able to catch fall overturn (find more information on lake turnover in our LakeKeepers manual) then we recommend conducting profiles in mid-January, mid-February, mid-March, and right after spring turnover (which usually occurs within 2 weeks of ice-off). If you are unable to complete all of these, we recommend a minimum two under ice profiles over the winter. One profile around mid winter, and another profile late in the ice cover period. If you are unable to catch fall overturn, then conducting an additional profile as close to ice on as possible would be ideal.
However, it is vital to note that monitoring lakes in the winter can be very dangerous and it is essential you have a proper safety protocol and basic knowledge about working on ice before attempting any winter monitoring. Never work or travel on frozen lakes without a partner. At minimum, wear a floater jacket, but a survival suit is preferable, and each person should have a pair of retractable ice picks (BCLSS, 2022). A good resource to begin learning about ice safety is the Adventure Smart website.
Tips for Using Your Instrument in Winter
- Go out on a warm day in the afternoon
- Calibrate at home prior to heading out to the lake
- Keep your meter from freezing as this can damage both external & internal components
- Keep your instrument inside your jacket or in an insulated bag with heat packs until deployment
- Allow sufficient time for your probe to reach temperature equilibrium when placing in the water due to the extreme difference in temperature from the warm environment to the water. One minute is recommended but your guidance should be when stable readings are achieved
References
BC Lake Stewardship Society (BCLSS) 2022. LakeKeepers Manual. A Guide to Lake Stewardship and Ecology in British Columbia. Retrieved January 5, 2026, from https://www.bclss.org/programs#lake-keepers-manual
Truelson, R.L. 1997. Water quality criteria for dissolved oxygen. Prepared for British Columbia’s Ministry of Environment, Lands and Parks, Water Management Branch, Victoria
Wetzel, R. G. 2001. Limnology: Lake and river ecosystems (3rd ed.). Academic Press.
