Most of the bad things that end up in freshwater lakes, like pollution and muddy silt, come from the lake's catchment area. This is all the surrounding land where rain drains down into the lake. To get clean water full of plants and animals, we work with the landowners to manage the land around the lake, in ways that are good for the water in the lake.

Bassenthwaite Lake is just more than 5 km sq in area. But its catchment area of 250 km sq means that anything on this huge area of land that can dissolve in water - farm chemicals, fertilisers, animal poo, sewerage and even mud and silt - will get into the lake water.

Nutrients – fewer are better!

A lot of the land around Bassenthwaite is farmland. Farmers want nutrient-rich ground as it makes the grass grow more, so their sheep and cows can eat more. They add fertilisers to the ground, sometimes artificial, sometimes natural, like manure.

Also around the lake are towns and villages. People create nutrient pollution, too. Washing machines, dishwashers, even shampoo can all contain phosphorous that goes down the plughole. It ends up at a sewerage treatment works before entering the rivers that lead into the lake. The sewerage works takes a lot of the pollution and nutrients out, but not all.

Once these extra nutrients get into the water, they make tiny plants called algae grow. A lot. Sometimes in the summer the algae grow so much that the lake water looks green!

We have been working with landowners to reduce the fertilisers they put on the land. And working with local communities to tell them about the problems the extra nutrients cause for the lake plants and animals.

Cutting down plants to stop the alien invasion

One Himalayan Balsam plant can produce upto 800 seeds

Most plants around the lake shore are good news. Their roots stop the soil and mud washing into the lake water, they provide a home for insects and birds and some of the plants around Bassenthwaite are special, rare species, like globeflower and saw-wort.

But alien plants are bad news.

Alien plants haven’t come from another planet, but they usually have come from another country or another ecosystem. Where they live normally there are animals to eat them and other plants to compete with them, which stops them growing too much. But the alien plants that have made a home on the shores of Bassenthwaite don’t get eaten as much and our native plants can’t compete with them, so they grow, and grow and grow. When alien plants get out of control like this, they are called an invasive species.

Himalyan Balsam and New Zealand pygmy weed are two aliens that have landed at Bassenthwaite. We're working hard to remove them. We even organised special 'balsam pulling' days where volunteers tug the plants out of the ground before they set seed. We will keep working on removing these plants for many years, and perhaps eventually eradicate them and plant native species instead.

Further information