antifouling - seawater>freshwater

[Grehan]

Is there any "real" difference (I guess there must be something, but for mere mortals . . .) between antifouling for seawater use and inland waterways use?
Down here in Spain we can't get freshwater stuff . . will normal sea stuff be ok (enough) when boat goes (almost immediately) into fresh water?

Thanks in advance for any words of wisdom.

 

[sailorman]

seawater a/f will be stronger therefore should be better