What is the fine-grained topic of the following text: Colorado Parks and Wildlife and US Forest Service volunteers rescued green cutthroat trout on July 20 from the lower prong of Hayden Creek due to biologists' concern that ash and sediment from the Hayden Pass fire could cut off oxygen and food supply for these fish. Only return the topic.
Rescuing green cutthroat trout from Hayden Creek due to potential threat from fire aftermath.