This is a map of lakes — 659 of them, to be exact, each one sampled, analyzed and compared to produce this kaleidoscopic belt stretching from coast to coast. And while this map won’t show you where to find Alberta’s famed Lake Louise, for example, it will show you how healthy Rocky Mountain lakes are and how many people use them.

A team of researchers from the Université de Montréal led by professor Roxane Maranger created this first ever “social-ecological” map of Canada’s lakes. To do this, the team examined three data sets to amass a deeper understanding of the health of lakes in 11 southern Canadian ecozones. The team analyzed the biophysical and chemical characteristics of each lake, the threats to its health, and how people use it recreationally.

The first step was physically sampling each lake, a painstaking task undertaken for the Canadian Lake Pulse Network (of which Maranger’s lab was a part) from 2017 to 2019. The breadth and methodology — a true cross-country sampling — made for a mountain of comparable research to sift through.

One of the biggest challenges in Canada is that because so many jurisdictions measure water quality, the collected information is disjointed, says Maranger, Canada Research Chair in Aquatic Ecosystem Science and Sustainability. “So the intention was to go and take a snapshot view of as many lakes as possible, and do it in a very harmonized way so that all the data were measured in the same way. Then, [all the data] would be comparable.”

Once the sampling was completed, researchers focused on determining the extent to which various environmental threats have altered each lake. It turns out indicators of a healthy lake in the boreal are different than those in the Prairies. For example, says Maranger, lakes in the plains region are naturally nutrient-rich by virtue of the composition of the soil and bedrock, while lakes in the continental region atop the Canadian Shield tend to have a lower pH.

The team identified broad lake regions — continental, Atlantic, mountains, plains and Pacific — and selected healthy and “minimally altered” lakes as baselines. As they analyzed the rest of the lakes in each region, they compared the collected data to the baseline lakes.

Regardless of their natural differences, the lakes identified as “altered” had two things in common: each had been damaged by increased nitrogen (a run-off from fertilizer and sewage wastewater) and chloride from road salt.

A stark, though consistent, pattern emerges: human activity is the problem. As cities expand and farming intensifies, the nearest lakes and their watersheds invariably come under increasing pressure from humans and the pollutants we create.

Because this map communicates the overall health of the lakes in an easy-to-read format, the researchers hope it will help both policy-makers and the general public to better understand which lakes are most threatened — and most popular. They can then use this data to pick priority sites for conservation and restoration.