Abstract
Observations were made on several hydrological features of Bay of Islands during 1970 to 1971. The topography of Bay of Islands allows for a gradual change from estuarine to oceanic conditions within the harbour. Monthly means of sea surface temperatures ranged between 15°c and 23°c, and some sea stratification was observed during summer. Salinities in the main basin were about 35.5‰; water transparency ranged from 2 m to 6 m by Secchi disc in the estuaries, to more than 15m in outer basin areas. Dissolved oxygen content was high, usually exceeding 100% saturation in surface waters. Water circulation within the bay appears to consist of an anti‐clockwise movement of at least the surface water, induced by a north‐west moving current, possibly derived from the East Auckland Current. The observations suggest that, except; for the estuarine areas, Bay of Islands is hydrologically a fairly homogeneous, well‐mixed body of water.