Do navy seals swim in S.American or African rivers?

i was just wondering what they would do in times of war in Australia, the Amazon or Africa for operations that would include entering the water and swimming, because these places are almost suicidal to enter the water because of crocs, hippos, poisonous animals etc. do they stay out of the water in these dangerous places? i know they were in the water in the Vietnamese rivers but there arent any dangerous animals in those rivers. the amazon isnt so bad for really dangerous water animals tho but there is some tricky **** in the amazon waters.