depends on width of stream really and how much flow you want.
The height is the main thing or what they call "the head"5ft would slow any pump but I guess a 2000gph pump would still create a good flow.
I broke something ealier on the UV so pump is temp just flowing into pond and I just went out and lifted the pipe to 5ft and I didnt notice much slowing, in fact I gat water everyewhere.....!