The decision was personal and McLean had tendered her resignation.
She was an independent director of the state-owned power company, which operates nine hydro power stations on the Waikato River, and has growing geothermal production in the central North Island.
On the Waikato, its iwi dealings are with Tainui, whose king, Tuheitia, called a national hui to press the government on the Waitangi Tribunal recommendation that iwi be offered a "shares-plus" deal to cover off Treaty of Waitangi claims before MRP's partial privatisation.
That followed the government's decision to postpone the first of three planned share floats from the last quarter of this year and target the second quarter of 2013, to give time for the politically charged issue to be resolved.
"We thank Parekawhia for her time on the Board and wish her every success in the future," MRP chairwoman Joan Withers said.
Maori claims to water have created uncertainty about both the sale of state-owned electricity companies and the future cost of water.
The Crown and Waikato-Tainui signed a deed of settlement in August 2008, providing a $210 million clean-up fund and co-governance over the Waikato River.