So the reason why this particular water is blue is the same reason why many water sources derived from melting ice or glaciers is blue - fine rock particulate matter (silt and clay) scatter the light to give its characteristic blue colour.

While copper salts do commonly form blue solutions, the amount you would need for them to be this blue would indicate an environmental hazard.

Edit: spelling. Also, the rock particulate matter os derived from glaciers and ice masses, grinding on the underlying rock as it moves and slides past on its way down the valley.