Nothing Can Undo Damage To Lakes Once It Begins

Taupo Times, Volume XIV, Issue 58, 27 July 1965, Page 1

Nothing Can Undo Damage To Lakes Once It Begins

Experience overseas had shown that nothing could be done to undo the damage caused by over-fertility of lakes which had deteriorated from clear water to turbid,~ Dr G. R. Fish, of the Marine Department, Rotorua, said in Taupo on Saturday. Dr Fish spent the weekend giving series of lectures on the ecology of lakes. He devoted much of his time to the deterioration of Lake Rotorua and said suhseguentlg, that findings of work done on the Rotorua lakes could well he applied to Lake Taupo.

Because lakes acted as settling basins for debris, hnmus and dissolved salts, their fertility increased according to the amount of material supplied to them. "Inevitably, human activities have a significant effect on lakes," he said. "Undeveloped country is ploughed, drained and manured, thus providing lake catchment water with much additional nutrient materials, which, of course, increases the fertility of the lake and accelerates its evolution." It was this development of the growth cycle of plants and small organisms in the lake which reduced the amount of oxygen avail-

able and so ruined the waters for trout. It was a never-ending cycle with the ultimate result that weeds and land plants took over and the lake eventually disappeared as such. Attempts had been made in Switzerland to stop the cycle and return the lakes to their previous clear state. However, although deterioration had been slowed down, it was not possible to undo the damage already caused. Dr Fish instanced the lakes Ngapouri and Okaro in the Rotorua district on which studies had been based for the past eight years. He said these showed

evidence of very rapid deterioration with the development of the surrounding farmland and that the few trout left were of relatively poor quality. "There is little doubt that they would not survive competition from another . fish species which was more suited to the type of environment now existing in these lakes," he said. Bass, carp and roach could survive in these conditions where trout could not.