The green colour of the sea in Mallorca which can sometimes appear is the result of an accumulation of algae. This is itself the consequence of an increase in the water temperature combined with nutrients in wastewater that are from outfalls or leaks.
This has been the case at beaches such as Sant Elm in Andratx, Cala Marçal in Felanitx, and Cala Llombards in Santanyi.
A way of addressing this is with the use of hydraulic pumps that create a water recirculation system. However, the environmental group GOB maintains that the pumps merely disperse the algae. The risk is that the algae spread and reach other coves. In addition, says GOB, there is an increase in the turbidity of the water because sediment is removed, while there is also an acoustic impact.
GOB want a debate as to the suitability of hydraulic pumps. In a statement they say: "Studies are needed in order to obtain objective data that evaluate the impact of this system on the environment. We have chosen to invest in a system. But its effectiveness and the real magnitude of the impact on the ecosystem are unknown." There is also an issue of energy consumption to take into account.
"The definitive solution involves correct sewage connections, the separation of wastewater and rainwater, and the adaptation of treatment plants."
In general, these algae are not toxic and therefore not harmful. The green colour tends to be accentuated over the course of a day.