So...water temps in march are gonna be chilly. October, same ball park...kinda depends on how late the summer runs. The website is good some of the time...just check the date, otherwise you can call in during business hours and they'll tell you. I usually go in june/july. It can vary from year to year. Water has been low the last few years so it's been warmer than normal, but when I went in may, it was chilly, but ok when the air temp was 90. As for OHV's, the sand and fun stuff is on the other side of a barbed wire fence (at least there used to be fence) from the south camping area. So...some people will set up camp...and park their trailer just on the other side of the fence from their campsite. I've never camped in there though so I don't know what the rules are, i've just seen folks do that. St. George is a wonderland of trails and such, even with all the expansion. I'd strongly recommend going to the end of river road and out into AZ, also go out to black rock road and there's some steep, fun trails taking you down to the Virgin River bank. Have fun down there! I'm jealous!