The river rises on the northern slopes of Mount Tongariro, one of the three active volcanoes of the central plateau, close to Lake Rotoaira.

This toxic water entered the Whanganui River and had the effect of killing much of the fish life downstream.

When Mount Taranaki left the central plateau for the coast, the land was split open, and the river filled the rift.

The Whanganui River was an important communication route to the central North Island, both for Māori and for settlers, despite many stretches of white water and over 200 rapids.

One of Hatrick's original boats, paddle-steamer PS Waimarie, has been restored and runs scheduled sailings in Whanganui.

Local iwi first petitioned Parliament in the 1870s,[9] and efforts have since been made to safeguard the river and give it the respect it deserves.

For the same reason, the river has been one of the most fiercely contested regions of the country in claims before the Waitangi Tribunal for the return of tribal lands.

The Whanganui River claim is heralded as the longest-running legal case in New Zealand history[10] with petitions and court action in the 1930s, Waitangi Tribunal hearings in the 1990s, the ongoing Tieke Marae land occupation since 1993, and the highly publicised Moutoa Gardens occupation in 1995.

[11] On 30 August 2012 agreement was reached that entitled the Whanganui River to a legal identity,[12][13] a first in the world,[9] and on 15 March 2017 the relevant settlement was passed into law (Te Awa Tupua (Whanganui River Claims Settlement) Act 2017) by the New Zealand Parliament.

[14] Chris Finlayson, the Minister for Treaty of Waitangi Negotiations, said the river would have an identity "with all the corresponding rights, duties and liabilities of a legal person".

[20] See Controversy over Wanganui/Whanganui spelling Native fish species in the river include Cran's bully, upland bully, climbing galaxias (kōaro), longfin and short-finned eels, pouched lamprey, shortjaw kokopu, torrentfish, New Zealand smelt[21] and black flounder.

[21] Blue duck (whio) populations can be found at the junction of the Whanganui River and the Mangatepopo and Okupata streams.

[24] The Nankeen night heron established roosts along the Whanganui River in the 1990s and is breeding in New Zealand only in this location.

PS Waimarie operates on the lower stretches of the river, including dinner cruises to Avoca Hotel at Upokongaro and trips to Hipango Park for overnight camping.

[32] The flow of the river has been altered with the diversion of water from the headwaters by the Tongariro Power Scheme and into Lake Taupō.

This may have been a contributing factor to the demise of the raft race and means river boats can no longer make the entire trip to Taumarunui during the drier months (see below).