Removal methods are difficult and with varying levels of success. Mechanical removal is costly and time consuming and using herbicides is contrary to good environmental practice.
Preventative methods are more successful. The use of barley straw bales is widespread. When barley straw is put into water, its cellular structure starts to break down or decompose, slowly releasing chemicals which inhibit the growth of algae. Barley straw should be placed in early spring and replaced approximately every four to six months or sooner if the straw fully decomposes before that time.
There are several commercial water treatment options to reduce blue-green algae including the use of ultrasound, aerators, and mechanic removal.
Report the occurrence to the local council Environmental Health department. They should then place suitable warning signs around the affected area to warn local residents and visitors.
Environment Agency have an incident hotline on 0800 807060 where incidents of blue-green algal blooms can be reported. They also have an information leaflet on blue-green algae.
You should record the presence of invasive species on a national database. You can record online at the Non-native Species Secretariat website. You should also alert the appropriate land owner, council and or management body to the presence and location of this plant.