Federal environment department officials did not become aware of the impact of South Australia's algal bloom until "towards the end of May" when they had their "first formal contact" with the South Australian government, a Senate inquiry has heard.

Officials from the federal environment department fronted a Senate inquiry on Wednesday, where they were grilled over the speed of their response to the algal bloom.

The inquiry heard federal Environment Minister Murray Watt was first formally briefed about the bloom on July 11 — about two months after he was sworn into the portfolio.

However, a South Australian government spokesperson said in a statement that state and federal government agencies had been working together since the bloom was detected in March.

"The former South Australian e

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