I have a problem with calculating the length of the main river in a network of rivers. I am only interested in the main stem length. Problem is that the river only consists of line segments and many side-rivers I am not interested in. Do I have to calculate this manually by using the "Identify" tool or are there easier options? I am going to use this on many different rivers so I hope there are more efficient ways to sort this out. If so, can you give me a little guide or point me in the right direction?