Hi!
What kind of rescue equipment do you use if the plane gets stuck (or crash) on the water drifting in the wrong direction? I'm considering making a small styrofoam raft and attaching my Bixler on top of it to use as an RC-rescue boat. But the risk is of course that I will end up with two drifting planes instead of one...
Perhaps attaching a fishing line in the tail of the rescue boat to be able to pull it back if it gets stuck in seaweed or stuff...

Welcome to RCGroups.

So far I just keep my fingers crossed

But if you try the following, there are a few threads on rescue boats, -

If you go back to the main Waterplanes forum page, on the right hand side is the Search this Forum, if you type rescue in there, set it to Search Threads, then click Go.

You should get a list of threads with rescue in their titles.

Also further down this page is the Similar Threads list, sometimes there may be a handy thread there.

Had to take a pic to show this one, I have tons of pics of my other boats. I don’t go anywhere without this boat. It has pushed most of the boats in my club. Every time I put an airplane in the water this little work boat is standing by ready to rescue. It has pushed my PBY, just practice, my Icon, but not my Skorsky S39.
It’s 19” long has a super cub motor and gear box, tazer 15T speed control. Has plenty of power and can creep along, even steers in reverse.
I can send more details if you like.

chasronw is right. Usually on a thread like this someone comes up with a half airboat/half forklift. WAY too complicated.
Use a simple boat.
I like to attach a fishing line to the boat, drag the line out with the boat and loop around the plane, then drag it back in with the fishing line and/or the boat power. Some have fabricated floating grappling devices to snag the airplane. The only reason I don't just push the boat as my first choice is that it is hard to find a spot to push against a downed airplane that doesn't make you just go in circles.

Jim that’s an art, but a piece of foam pipe insulation on the bow will grab and make pushing easier. Some make a pushing rack from PVC pipe and foam insulation, two legs fit the side of the pusher boat and extend out front to wrap or push the boat/airplane. That works great. Care must always be taken not to damage or worse sink the boat/airplane. See the pic.
A Springer Tug has a flat front and push bumpers, easy to build and find plans for.

I built an inexpensive rescue rig using a Traxxas Blast, PVC and a swimming pool "noodle". It's not fast, but works well and the boat doubles as for something for my daughter to enjoy while I'm flying or driving my RC boat!

Best one I've seen: a radio-controlled motorized duck.

Worked great and had us in stitches on the shore.