1. Management of toxic algae in Danish lakes 2. LakePromo Seminar - April 20–22 2005 Bad Saarow - Germany Mette Bramm - County of North Jutland

2. Massive algae blooms recurring problem every summer in lakes aestheticaesthetic problem recreational activitiesinconvenient for recreational activities More serious… some algae produce toxins which may present a health risk!

3. Cyanobacteria - main producers of toxins in lakes type: cyanotoxins (liver toxins) 2/3 of Danish lakes contain cyanotoxins responsible genera: mostly Anabaena and Microcystis LD 50 < 50 µg/l (mice) Relative toxicity 1 : 122 Amanita muscaria Anabaena circinalis

4. Effects of cyanotoxins… If consumed, inhaled or by direct contact symptoms can be…. skin irritations, stomach ache/cramps, diarrhoea, fever, headache etc. pneumonia, liver cancer, hepatitis, gastric catarrh etc. - depending on the degree of exposure… Symptoms first recognized in 1833 Fauna deathFauna death Lessserious Veryserious

5. Management of massive algae blooms municipalitiescounties - a co-operation between municipalities and counties supervision of lakes used for recreational purposes purposesmunicipalitiescounties national* and regional surveillance of lakes surveillance of lakes *fulfilling the obligations of The National Action Plan of Water Environment and The Water Framework Directive sometimes the same

6. Action programme at critical blooms Supervision of lake bath water Reports of blooms Weather forecasts Advises against bathing or prohibition Routine supervision continued Risk assessment by counties Risk assessment by municipalities national and regional surveillance of lakes Increased occurrence of toxic algae No or few toxic algae

7. Risk assessment - signs of potential toxic algae In the field…. coloring of the water, low transparency, accumulation of algae, dead animals (e.g. fish, birds) In the laboratory… chlorophyll-a levels > 50 ug/l, dominance of cyanobacteria especially genera like Microcystis and Anabaena Toxicity tests… an exception to the rule, as cyanotoxins are always present

8. Informing the public - an important task General information… - about algae, health risks, signs of blooms, good bathing advises, recommendations etc. - done through brochures, internet, libraries etc… Boards at the lake site… - all year round: general information - when potential toxic algae blooms are detected: warning/prohibition boards Warning!Warning!

9. Lake Hornum

10. Algae blooms - bathing forbidden Reduction in diffuse loading

11. Algae blooms - bathing forbidden

12. Thank you