The algae occurs naturally in certain conditions
A campaign aims to tackle potentially toxic algae on a Snowdonia lake by asking people to consider their use of washing machines and dishwashers.
The algal blooms at Llyn Padarn, near Llanberis, have the potential to kill fish, animals and birds.
Environment Agency Wales wants to reduce the nutrients entering the lake from washing machines and dishwashers.
People in Llanberis are asked to only use the appliances when full and not use more detergent than needed.
Because algae feed on nutrients in the water, reducing the amount of food available can help to combat the growth of algal blooms in the lake.
Meic Davies, of Environment Agency Wales, said the agency was asking the people of Llanberis to help "because this is very much about improving the quality of their environment and helping the local economy".
He said: "We know that around 25% of nutrients in sewage effluent come from modern detergents which we use in washing machines and dishwashers.
"These in turn provide food for the algae to form these blooms which can release toxins into the water.
"This is part of a wider campaign which looks at all sources of nutrients coming into the lake, and we believe this can have a positive impact on water quality in the lake."
The campaign is calling on people to:
- Only use washing machines and dishwashers when they are full
- Only use as much detergent as recommended on the pack
- Use a detergent with reduced or no phosphate.
Leaflets will be distributed to every household in Llanberis and Nant Peris, and posters will be put up locally.
The agency has also set up a local group, chaired by Alun Ffred Jones AM, to look at how to solve the problem of algal blooms in the lake.
The problem also exists at other lakes such as Llyn Llygeirian, near Llanfechell on Anglesey, and Llyn Tegid in Gwynedd.
The algae occur naturally in certain conditions - such as warm, still weather with direct sunlight - and has the potential to produce toxins when it blooms.