Water Quality Report - 2025

Cross Lake’s water quality in 2025 was very good, although we had a few ephemeral blooms and a lake-wide algal bloom around October 15th. Our water clarity average was 3.8 meters (~12½ feet), much deeper than our previous annual average of 2.7 meters (~9 feet). We take biweekly Secchi Disk Transparency (SDT) readings at Station 1 (the “deep hole” close to the public boat launch) biweekly.

 

Phosphorus (P) is a plant nutrient that in excess from the watershed causes algal blooms. The total phosphorus (TP-C) average of the sample results in 2025 was 13 parts per billion (ppb), much less than our previous annual average of 17 ppb, and below our Watershed-Based Management Plan (WBMP) 10-year goal of 14 ppb. TP-C is the total phosphorus in a “Core” sample collected to a maximum depth of 10 meters (~33 feet), sometimes less. TP-G is a “Grab” sample collected one meter off the bottom of the lake, which we collect in August and September only. The TP-G results tend to be higher than the TP-C results due to phosphorus released from the sediment.

 

Algal blooms are more likely to occur when chlorophyll-a (Chl-a is the green pigment in plants, including algae) is above 8 ppb. The average in 2025 was 7.6 ppb; our WBMP 10-year goal is 4.7 ppb.

 

We hope the improvement in water quality parameters continues. It hopefully is due in large part to the great work the NRCS in Fort Kent is doing with the Cross Lake Watershed National Water Quality Initiative (NWQI) funding and our grant work. Many thanks go to Alex Zetterman, NRCS District Conservationist, and his staff! We need at least 10 years of data to establish a trend.

 

We also take dissolved oxygen (DO) and temperature (T) profiles at Station 1 biweekly with the water clarity readings and monitor Station 3 in the north end of the lake monthly.

 

The colorful DO Profiles chart shows that in the spring and fall when the lake is mixed, the DO remains high throughout the water column, but in the summer when the lake "stratifies" into different temperature layers, deeper than 10 meters or so the DO goes below 5 parts per million (ppm) (called "hypoxia"), which is stressful to coldwater fish (salmon & trout), and is depleted to less than 2 ppm ("anoxia") at deeper levels, where coldwater fish cannot survive. That's why summer fishing for trout and salmon is generally not good in Cross Lake, although white and yellow perch and other “warmwater fish” do fine. In 2025, the summer hypoxia occurred at a much deeper level (~10 m) than in 2024 (~5 m), which is a good thing.

 

We hope you find this 2025 water quality information helpful!