The River Tay is the longest river in Scotland, running for a total of 120 miles. It rises in the mountains of Perthshire and flows eastward to the Firth of Tay. The River Dee is the second longest river in Scotland, running for a total of 90 miles. It rises in the Cairngorms and flows eastward to the North Sea. The River Tweed is the fourth longest river in Scotland, running for a total of 97 miles. It rises in the Lowther Hills and flows eastward to the North Sea. The River AYR is the sixth longest river in Scotland, running for a total of 75 miles. It rises in the hills of South Ayrshire and flows westward to the Firth of Clyde.