Observations on excessive weed growth in two lakes in New Zealand

Abstract

Weed growth during recent years in lakes Rotorua and Rntoiti has become sufficiently abundant to threaten normal use of lacustrine facilities such as angling, boating, etc. Data referring to the ecology of the weed are presented from the results of a survey made during 1961. An arsenical herbicide failed to control the weed growth, possibly because of the low temperature of the lake water, or of an acquired tolerance to the poison since high arsenic levels were found already to exist in the plants and bottom deposits of the lakes. The dangers to the trout fishery of further eutrophication in these lakes arc discussed.