Examples of New Zealand estuaries impacted by eutrophication. Left: High biomass of nuisance macroalgae piled on the shores of the Avon-Heathcote Estuary in Christchurch. This photo was taken prior to the diversion of Christchurch City’s wastewater out of the estuary to an ocean outfall in 2010 when estuary nutrient levels were very high.
Right: High abundance of suspended microalgae (phytoplankton) and clumps of detached macroalgae in Kakanui River estuary (Otago). This photo was taken during a period when the estuary was closed to the sea, causing poor flushing and high nutrient build-up in the estuary from river inputs.