The Crown's actions contributed to the pollution of Lake Horowhenua and Hōkio Stream, the Waitangi Tribunal has found.
The tribunal has upheld claims by Manawatu iwi Muaūpoko, which focused on their lands and waterways in Horowhenua.
In its report, released today, it found serious breaches of Treaty of Waitangi principles in relation to Crown actions and omissions involving Lake Horowhenua and the Hōkio Stream.
The tribunal said the Crown took an unusually active role in both waterways and it was complicit in their pollution and environmental degradation.
It said in the early 1900s, the Crown turned Lake Horowhenua - the bed of which belonged to Muaūpoko - into a public recreation reserve, giving control of it to a domain board.
According to the tribunal, this was done without the full agreement of the Muaūpoko owners.
Following this, the tribunal said a series of significant treaty breaches followed in the way the lake has been controlled and administered, including an inadequate attempt by the Crown to remedy these matters in 1956.
It recommended the Crown fund and establish a legislated Muaūpoko governance structure to act as kaitiaki for the lake and the stream.
The tribunal also said the Crown had purchased the Levin township site in a way which was significantly unfair to Muaūpoko.
It said the local iwi were subjected to a number of significant treaty breaches in the 1890s that deprived them of their lands and rendered them landless by the end of the 20th century.