What are the rules while taking a bath and performing rituals in a river? Should we take a bath at home before proceeding to other places for bathing in the river? Is it applicable to take a bath at sea as well?

Bathing in holy rivers is considered special and it is not a must that one has to travel to another place to take a river bath. Taking a bath in the river eradicates taint and then one can perform sankalpam and take a bath once again in the same river. The river keeps flowing hence it is considered fresh water.
While taking bath in sea, one has to bathe beforehand, and one should not touch sea water with taint.