The flow of water in Montana's rivers is lifeblood for its economy, both through tourism and agriculture. Montana's trout and its $300 million recreational fishing industry depend on cool waters flowing from melting snow high in the mountains throughout the summer. Irrigated crops play a prominent role in Montana's $2.4 billion agricultural industry, and these crops rely on the same strong river flows during the summer when soils are driest and plants thirstiest. But a broad trend is changing the way streams and rivers flow in Montana, as temperatures across the state have been rising.

Warmer temperatures mean that snow in the mountains begins melting sooner. Earlier snowmelt means less snow remains during the summer months - especially late in the summer - which translates to less water flowing down Montana's rivers. This means less water for irrigation, and slower flows in streams. Slow-moving water heats up more easily when the weather is hot, so slower summer flows mean more opportunities for water to get above the lethal 78 degree F threshold for trout. Beyond this, Montanans also have to cope with increased wildfire activity and more outbreaks of tree-killing insects. Both trends, which have been linked to human-caused warming, cost the economy dearly.