Watercare is under fire for keeping a $20 million deal with Waikato-Tainui under wraps.

It's been revealed the Auckland Council-controlled water provider last year signed up to paying $1 million a year, for two decades.

The money will go into research and environmental projects in the Waikato River and catchment.

It's on top of $40 million paid for clean-up projects under Watercare's river-consent agreement.

Watercare chief executive Dave Chambers says they could've been more open.

"As things have unfolded today - certainly if we had our time again, we would have done things in a different way." 

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