2009 November: Pesticides Suspected in Dolphin Deaths. Pesticide: Dieldrin.

Nov 2009: DAYS after authorities revealed the deaths of six dolphins in Perth's Swan River within four months, scientists said up to eight had died near Bunbury in the past two years...But he said the recent deaths within the Swan River pod, which have occurred since June this year, had happened in a similar environment and could provide some clues.
At least three of the dead Swan River dolphins were confirmed to have high levels of the highly toxic pesticide dieldrin, which was banned in 1988.

Nov 2009: DAYS after authorities revealed the deaths of six dolphins in Perth’s Swan River within four months, scientists said up to eight had died near Bunbury in the past two years…But he said the recent deaths within the Swan River pod, which have occurred since June this year, had happened in a similar environment and could provide some clues.
At least three of the dead Swan River dolphins were confirmed to have high levels of the highly toxic pesticide dieldrin, which was banned in 1988.

https://www.heraldsun.com.au/news/breaking-news/pesticide-suspected-in-dolphin-deaths/story-e6frf7kf-1225799861802