The river is your river of emotions - you are floating above them. Was the boat floating downstream, or was it anchored or moving against the current?
A snake might symbolize an emotion that feels treacherous to experience. What emotions are lurking deep inside that are just waiting for an opportunity to leap up and bite you like a jolt of electricity?
Our legs are what we use to carry ourselves from place to place (at least on land). What feelings and emotions are submerged deep within you that if they should emerge feel like they might hamper your ability to carry yourself?
Something within wants to be noticed and dealt with, and it would seem to be significant. I would consider this a dream encouraging you to take the time to look within - to "wake up" to whatever unfinished business has been on the back burner. It is fortunate to have dreams guide us through the process of integrating submerged, unresolved experiences that are in need of resolution for our highest good.