I have a boat with the Mercury 175 hp SportJet engine... I haven't had any
freshwater weeds clock the jet, but I have had some seawead clog it while
offshore... Mine does not have a way to automatically get rid of it, so I
have to jump over the side, swim under the boat, and clear it by hand...
Since I'm usually going offshore for diving anyway, this is not a big
deal... I understand that the newer boats have a way to automatically clear
the grate...

The only thing that I have had clog it during freshwater operations was a
tubing tow rope that my S.O. drove over when she was pullng me... It wrapped
around the impeller and was not fixable while in the water... I had to get a
friend that was out with us on a jet ski to give me a tow back to shore and
once home, I was able to get it untangled in an hour or so by taking the
grate off and unwinding it from the impeller...

I've found that you can get into some really shallow areas with a jet
boat... I think my boat has a 10" draft (don't remember if that is up on
plane or just sitting still in the water), but it definitely has less of a
draft while up on plane since I've been in places where I was able to easily
maneuver while on plane, but when I powered down, it settled on the
bottom...