How can i stop my dog from wanting to go in water when off lead on walks?

He is a 4 month old GSD and up till a week ago didn't have any interest in the water, but i was walking him through my local woods and there is a stream running though it, it was no deeper than ankle to knee depth and my pup ran over there and had a drink then jump in walking about trying to bite the water. I found this endearing at the time and i wasn't bother he was doing it. all it would mean is i would have to dry him when i got home.

But on sundays the whole family come along on the walks as well, so we dry to these bigger woods where there are lots of other dogs and people ( i thought this would be good socialization on top of puppy training) and there is a river and still not waste high it is fast flowing at parts and i don't fancy much jumping in when my dog struggles to get out.

thankfully due to a good recall he didn't jump in i just had to keep calling him back when he tried to get to the bank or something not too high to jump off.

If i stopped him going into the stream in the local woods would he eventually lose interest in the river or will i have to put him on the lead in them areas? thanks