The Supreme Court has heard that the Crown had a duty to fully explain what it was doing when it bought land and a riverbed from a hapu at the end of the 19th century.
The people of Pouakani want judges to rule that the sub-tribe owns a 32km portion of the Waikato River.
The lead lawyer for the claimants told the court on Tuesday that it was not obvious that the Crown was purchasing the riverbed near Tokoroa.
Ian Millard, QC told the court when Crown agents came to the Pouakani lands, no tribesmen spoke English, there were no schools and no missionaries, and local Maori would not have understood the purchase agreements.
He says it was up to government officials to tell the hapu exactly what the Crown was buying.
The court is being asked to explore whether the Crown acquired the sub-tribe's land with their full and informed consent.
Mr Millard went on to say that when the Crown built hydro dams from the late 1940s on, there was no consultation with tangata whenua.
If the descendants win, they will also seek ownership of the three hydro projects on the river.
A bus load of Maori elders has travelled to Wellington from Waikato to hear the case, which is scheduled to run for three days.