JIM O’Brien’s letter (August 2) highlights one of the contributing causes to the weed problem in Poole Park Lake. The fact of the matter is that it is caused by the process of eutrophication.

The activity of organisms in the mud are releasing nutrients to the water column. In particular, phosphates and nitrates, which promote excessive weed growth. Phosphorus and nitrogen compounds are then deposited in the mud again when the weeds die back. Thus it becomes a continuous cycle.

The only solution is to mud-pump the lake, as has been done on the Norfolk Broads. This of course would be very costly.

The islands of reed beds only aggravate the situation. When the reeds die back they too contribute to the nutrients in the mud. One has to ask the question; How much surface water pollution, if any, is adding to the problem? What monitoring is being done of the surface water and at what frequency?

DEREK SERCOMBE, Littledown Ave, Bournemouth