As we know, IRL water (rivers, lakes, sea) during war is something you really don't want to stay in. It's used as really effective natural defence. Bridges are really strategically important objects.
Now in AoS water slows you down only a little, and in exchange gives you 360 indestructible half-cover, from one to three sides full indestructible cover, makes you less vulnerable to nades. From my experience - it's really good idea to stay and camp in water, and that's wrong. Also bridges are not worth the effort, except those 1x1 bridges far from frontline.
Currently available tool to force people out of water is water damage, but many players don't like it and call it unrealistic.
So my suggestion is: don't allow (or make really inacurrate) shooting from water (including water near the banks). IRL, you can't really snipe while swimming, especially with 30kg on your back.