Plankton blooms are common in a number of freshwater lakes in the North Island where nutrient runoff has increased levels. This photograph shows a phytoplankton bloom in the right side of Lake Ōrākai, Hawke's Bay, and clear water in the left. Silver carp were introduced into the left side to control the growth of tiny floating aquatic plants known as phytoplankton. The fish are herbivores and feed by filtering phytoplankton out of the water. There are no self-sustaining populations of silver carp in New Zealand, although brood stock are kept in captivity.
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Fisheries New Zealand
Reference: A. D. Carruthers, Effect of silver carp on blue-green algal blooms in Lake Orakai. Napier: Ministry of Agriculture and Fisheries, 1986, p. 19
Photograph by A. D. Carruthers
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