Thank you for your question. There is more information that is needed to be able to answer this question appropriately, so it is important to speak with your doctor
. First, how long have your symptoms been lasting for? If you sent this question in within an hour of coming out of the river, then the answer would obviously have the potential to be very different than it would be if several weeks, months, or years have passed. Additionally, how cold the water was could also affect what the potential explanation is, and also how long you remained in the cold. Finally, any of your other medical conditions and whether or not you hit or leg or had any other trauma while you were in the water would also potentially explain or enhance the understanding of why your leg is still bothering you. Briefly, there are a few possible explanations. First, your leg, like the rest of your body, depends on blood getting to the tissues to stay alive. When the blood supply is limited, the nerves in the leg will begin to send a signal to the brain that something needs to change to increase blood flow. While cold could affect blood flow, the position can also affect this. Please speak to your doctor about your unique question and get the help you need.