The challenges

Over the past 50 years, concerns have been raised about the health of the lake, in particular algal blooms and bacterial pollution, potentially harmful to wildlife and humans.

Microscopic view of Blue Green Algae


Phosphorus and nitrogen are two nutrients that enter the lake from a variety of sources.  They have a similar effect to fertiliser, providing a food source for plants and algae. These nutrients come from wastewater, septic tanks, boats, waterfowl, grazing animals and fertiliser and from the sediments in the bed of lake.

Climate change

We are already seeing the impact of climate change on Windermere. The average temperature of Windermere has increased by +1.7C in the last 70 years (see reference). This, together with high levels of nutrients encourages algal growth and cyanobacterial blooms, leading to a number of issues within Windermere, including reduced visibility and lower dissolved oxygen concentrations, which can affect lake ecology.

Extreme weather patterns

Another symptom of climate change is more extreme or erratic weather patterns. Periods of very heavy rainfall or prolonged hot dry weather are becoming more common. Heavy rainfall increases the level of nutrients and bacteria washed into the lake, from highways, sewers, septic tanks and farmland. Prolonged hot sunny weather makes ideal conditions for algae to thrive.

Introduced Species

The deliberate or accidental introduction of new species into the lake environment can have profound effects when that species competes with others for food and habitat, or feeds upon the species already present. For example, we know that Ruffe have been introduced into the lake, but as yet do not understand the effects of this introduction.

Tourist numbers

The population living around the lake can double between winter and summer, putting an extra load of nutrients into septic tanks, wastewater treatment works and sewage facilities at campsites.