Naturally, the government went apeshit, passing a law to confiscate any remaining Māori property, with consequences we are still living with today.
Fast forward 22 years, and, in a case about rights over a specific part of the foreshore, the Supreme Court has recognised that the settler government hasn't actually stolen all the riverbeds either. The law the government relied upon to claim that it had - section 261 of the Coal Mines Act 1979 - didn't mean what they claimed it did, and in fact had essentially the same wording as the law the government relied upon to claim it had stolen the foreshore and seabed (section 7 of the Territorial Sea, Contiguous Zone, and Exclusive Economic Zone Act 1977). The interpretation of that sort of law as not expropriating existing customary rights was settled by Ngati Apa, and it applies to purported expropriations of riverbeds just as it did to the foreshore and seabed.
Of course, whether any particular iwi or hapu still owns any particular riverbed is a matter of fact. But the government can no longer simply deny it as a question of law. I wonder how long it will be before they go apeshit and use it to open another front in their racist hate campaign against Māori? And will ACT, who back in 2003 claimed to be the "party of property rights" and opposed retrospective expropriation, support or oppose a racist law change?