… a blog by Buglife Conservation Director, Craig Macadam.
It’s always great to get out for a walk, and there’s nowhere better for some mindfulness than at the side of some water. Saturday was a crisp winter’s day and my wife and I headed to the Lake of Menteith, Scotland’s only natural lake (the rest are lochs!). My plan was to look for some winter stoneflies (Capniidae) but I was thwarted by a bright green, swirling bloom of algae.
These blooms represent a visible symptom of nutrient pollution in our freshwaters. When excess nutrients enter water bodies, they trigger explosive growth of microscopic algae and cyanobacteria. Some species create unsightly conditions, while others produce dangerous toxins harmful to wildlife, pets and humans. The blooms also cause severe oxygen fluctuations – producing excess oxygen during daylight through photosynthesis, but depleting it to dangerous levels at night through respiration.
This nutrient enrichment, also known as eutrophication, can happen naturally in some areas, especially where large flocks of birds like geese roost for the winter. However, it’s mostly caused by human activities. The main culprits are phosphorus and nitrogen, which enter our waters through several pathways. These include runoff from agricultural fertilizers, livestock waste, discharge from sewage treatment plants and septic tanks, phosphate-based detergents, and industrial wastewater. Freshwater fish farms and fisheries can also contribute through excess feed and fish waste. Even forestry practices, like clear-cutting, can disrupt the natural cycling of nutrients and lead to increased leaching into waterways. Finally, air pollution from vehicle exhausts, industry and agriculture can deposit nutrients into freshwaters, adding to the problem.
The impact of nutrient enrichment ripples through entire ecosystems. Sensitive invertebrates like stoneflies and mayflies disappear, replaced by pollution-tolerant worms and midges. These changes can then affect fish populations and reduce the water’s ecological and recreational value.
Addressing eutrophication requires coordinated action. The forthcoming reviews of water management plans across the UK presents an important opportunity to tackle nutrient enrichment and promote nutrient neutrality across water catchments. Farmers should be encouraged to reduce runoff through buffer strips and improved nutrient management. Water companies must invest in advanced treatment technologies such as phosphate stripping. Local authorities can promote sustainable drainage solutions and stricter planning controls, while public awareness campaigns can help reduce household contributions.
Recovery takes time, but successful restoration projects show improvement is possible with sustained effort. As climate change adds further stress to freshwater systems, tackling nutrient pollution becomes increasingly urgent. We can create healthier freshwaters with thriving invertebrate populations by strengthening nutrient enrichment controls in the revised River Basin Management Plans. My search for winter stoneflies continues, but hopefully one day soon I’ll be able to find them again at the Lake of Menteith.
Main Image Credit: Algae at Lake of Menteith © Craig Macadam
