| Waihou River | |
| Name Other: | Thames River |
| Map: | NZ-Waihou R.png |
| Map Size: | 270px |
| Subdivision Type1: | Country |
| Subdivision Name1: | New Zealand |
| Subdivision Type2: | Region |
| Subdivision Name2: | Waikato |
| Length: | 150km (90miles) |
| Source1: | Mamaku Ranges |
| Mouth: | Firth of Thames |
| Mouth Elevation: | Sea level |
| Tributaries Right: | Ohinemuri River, Komata River, Hikutaia River, Puriri River |
| Bridges: | Kopu Bridge |
The Waihou River is located in the northern North Island of New Zealand. Its former name, Thames River, was bestowed by Captain James Cook in November 1769, when he explored 14miles of the river from the mouth. An older Māori name was "Wai Kahou Rounga". A 1947 Geographic Board enquiry ruled that the official name would be Waihou.[1]
The river flows north for 150km (90miles) from the Mamaku Ranges past the towns of Putāruru, Te Aroha, Paeroa and Turua, before reaching the Firth of Thames at the south end of the Hauraki Gulf near the town of Thames. In its lower reaches, the river and the nearby Piako River form the wide alluvial Hauraki Plains. Just before the river reaches the ocean, State Highway 25 crosses the river over the Kopu Bridge, which was the longest single lane bridge in the country at 463m (1,519feet) and the only remaining swing bridge on a New Zealand state highway. The bridge was infamous for the queues of vehicles travelling to and from the Coromandel Peninsula until a new two lane bridge was opened in December 2011. Tributaries include the Waimakariri Stream, Waiomou Stream, Oraka Stream and the Ohinemuri River.[2]
Many areas on the banks of the Waihou River were settled by Hauraki Māori, such as Oruarangi pā and Paterangi pā near Matatoki, and the Te Raupa pā and Waiwhau pā near Paeroa. The mouth of the river was famous as a location for pātiki (flounder) fishing.[3]
In 1879 Te Au o Tonga,[4] or the Falls of Awotonga, were destroyed by 200lb of dynamite to free the navigation of the river for shipping. There was a water column of 150feet. Other parts of the river had been cleared in the same manner in previous years.[5] Josiah Firth spent £7,442 to 1880, extending navigation for his Kotuku steamer, drawing 3feet, as far as Stanley Landing,[6] near Gordon.[7] By 1923 a 30feet launch could reach Okauia.[8] A 1925 report said there had once been a steady traffic.[9] Regular traffic on the river ended in 1947.[10]
In the 1910s stopbanks and floodgates were constructed along the Waihou River in order to protect farmland from flooding, including a canal constructed at the point where the Waihou River and Ohinemuri River meet, west of Paeroa. Further work occurred in the 1980s after extensive flooding in 1981.
The river supports large populations of rainbow and brown trout. A survey conducted in 2009 showed that the upper section of the river supported over 700 fish per kilometre.[2]
The water quality at Te Aroha is in the worst category for dissolved reactive phosphorus and also the worst 25% of all sites measured for other pollutants.[11] At Okauia the river is in the worst category for ecoli,[12] though the measurement may have been overestimated.[13] In the upper reaches of the river the main pollutant is phosphorus.[14] Water flows are measured at Te Aroha[15] and Okauia.[16]