Blue-green algae- the one most fresh water sailors are concerned about - may discolour the water so that it appears green, blue-green or greenish-brown. During calm weather the algae can rise to the surface to form scum - this may be like blue-green paint or jelly and may form flocs. Wind will make the scum accumulate on lee shores and sometimes the algae release toxins into the water. Thus, there is a greater risk of contact with toxins in shallow water where the algae are found in higher concentrations. (N.B They do not always release these toxins and it is not possible to tell from the concentration of algae whether they are producing toxins or not).
Some marine algae look like sewage but are perfectly harmless, although a trifle smelly!!! (This occurs when the algae blooms break down as the algae die and then form creamy-brown foam.)
Yes possibly, if contact is made with the algae toxins and affected water is drunk. The following problems can occur: 1) Skin contact - Rashes and eye irritation. 2) Swallowed - Vomiting, diarrhea, fever and joint and muscle pain. Although death has been recorded in animals venturing into thick concentrations of algae to bathe or drink the water, or licking the scum and deposits off their fur when coming ashore, effects on humans to date have been limited to illness rather than death.
Your Club Committee has been advised that, if the pond is affected by Blue Green Algae, sailing activities can still take place provided certain precautions are taken. The greatest risk is in shallow water where wind or current-driven concentrations of algae have built up. The scum on the waters edge is a particular source of toxic material.
To minimise contact with the algae, wear tight fitting clothing and avoid capsize in shallow water. Minimise any time in the water. Wash boat and clothing off with running water after sailing and wash clothes immediately after contact. If capsize righting drills have to be carried it is safer in deeper water where the concentrations of the algae are much smaller.
Concentrations of algae vary from day to day, hour to hour and minute to minute. In particularly, during hot summers, the Health Authorities may deem it so severe that they close the pond. Otherwise take sensible precautions.
Algae feeds off the nutrients leached into the water through farm fields (nitrogen and phosphorous). The only way to destroy it is to filter all the water and bottom of the affected water through copper. Highly expensive and not 100% guaranteed.
Dr Frank Newton (RYA Hon-Medical Adviser)