Most are in the languid waters of the inner gulf, such as here in the Waiheke Channel, where hundreds of placid anchorages make for some of the best cruising in the world.

Lurking beneath, however, is the invisible menace of life in the gulf. Over the past 90 years, sedimentation in the Firth of Thames have been increasing at rates ten times higher than other estuaries. Sedimentation is toxic to marine organisms, reducing diversity and abundance. If anything, rates of sedimentation in the Firth are expected to increase as rainfall events become more intense.