It is the firth of the rivers Waihou and Piako, the former of which was formerly named the Thames River, and the town of Thames lies on its southeastern coast.

In traditional legend, the firth and the greater Hauraki Gulf are protected by a taniwha named Ureia, who takes the form of a whale.

[2] The firth lies at the southern end of the Hauraki Gulf, southeast of the city of Auckland.

It occupies a rift valley or graben between the Coromandel Peninsula and Hunua Ranges, which continues into the Hauraki Plains to the south.

However, the firth overall is severely damaged by man-made influences, especially dairy-farm run-off, and has not recovered from large-scale mussel dredging over 40 years after the practice ceased (more information in the Hauraki Gulf article).