Under the Marine and Coastal Area Act 2011, claims had to be filed within six years. Around 150 claims for ownership, for thousands of kilometres of New Zealand's coastline, were filed in high courts around the country, before applications closed on Sunday.
However, Mr Paul says he was concerned some would be caught out.
"It seemed to me that many Māori may not have realised that they had until [the end of April] to register their application for their customary rights."
Mr Paul told Newshub that Māori would make better guardians of the foreshore and seabed than the Government.
"Governments in the past, [whether] by omission or commission, have failed to protect the quality and the quantity of our water."
He points to the fishing industry as a proven illustration of Māori being better guardians of our resources than the Crown.
"No Pākehā today is angry about the way the fishing industry is operated when Māori
are 75 percent shareholders,
"Every time they get a day off they can go fishing [and] all their rights as New Zealand citizens are protected."
Maanu Paul says under Māori management fracking, water bottling, dairy and industry pollution will be minimised.
Te Arawa Lakes Trust chairman Sir Toby Curtis told NZME he agreed with Mr Paul's stance, claiming Māori wanted a "more custodial" position over water.
"New Zealand is a resource to pass on to the next generation, not just sell on."
While Māori were granted some base rights in the 1992 Fisheries Claims settlement, including $150 million and a 20 percent quota, Mr Paul said that was only "partial recognition".
"The question then arises who should make the laws and regulations for the use of water, access to water and cost of water."
The New Zealand Māori Council is planning to establish a water commission to "take on those duties", granting access to every New Zealander.
"I have black hair brown-eyed mokopona. I also have blonde hair green-eyed mokopona. I need to leave a legacy where they both enjoy an environment that is sustainable forever."
The Crown has begun negotiating directly with those likely to have well-founded claims.
Anyone is able to object to a claim within 20 days of it being advertised.