CSIRO chief Larry Marshall said he only learned of the Turnbull government's plan to funnel $444 million for Great Barrier Reef research to a non-profit group in "a rumour", an admission leapt on by federal Labor as further proof the policy was "driven by electoral panic".

Dr Marshall told Senate estimates on Thursday that although he served on the chairman's panel of the Great Barrier Reef Foundation – and had attended each of their bi-annual meetings since becoming CSIRO head in 2015 – he had little inkling the organisation was about to become the main channel for reef research funding.

Larry Marshall, chief executive of CSIRO, grilled about the Turnbull government's Great Barrier Reef plan at Senate estimates on Thursday. Credit:Senate

He said he first heard informally of the April 28 announcement of a special partnership between the foundation and the government "probably the weekend before".

"It was a rumour that I heard," Dr Marshall said.