It is still too cold to swim in Northern California rivers, officials warned Thursday. Temperatures are in the 90s in Sacramento — but don’t give into the temptation to take a dip in local waterways. The record Sierra snowpack is melting, causing fast and cold currents longer than even regulars are used to. … Water flowing out of the Nimbus Dam into the American River is anticipated to be flowing “six times higher” than normal for the summer months at 12,000 cubic feet per second, the news release stated. Not only are rivers flowing fast, the water is cold, too.