[5] The river is naturally turbid and had low to moderate levels of phosphorus and nitrogen,[6] though it is among the poorer rivers for ammoniacal nitrogen, black disc and e coli measurements.

[7] Tiritiri Matangi peninsula, in the river's estuary,[8] is a protected area of international ecological significance, as it is an important stop for migratory seabirds.

[19] In 1938 the Hamilton mayor, John Fow, and Chamber of Commerce were reviewing plans for a new link to Kawhia.

A route through the valley, via Kaniwhaniwha[20] and Karamu was suggested and, by 1945, there was much backing for a 10 mi (16 km) long road on that route, which would have reduced the distance between Hamilton and Kawhia by about 20 mi (32 km).

[21] From 1923 Ōpārau was served by hydroelectric power, generated for the dairy[22] by a 33 hp (25 kW) turbine at Mangapapa Falls,[23] about 2 km (1 mi) upstream from the village.