One note about Antelope Marina - be prepared for a walk. Due to current water levels, the marina is over 1/2 mile hike from the parking lot. While the marina offers a golf-cart shuttle in each direction, they are not guaranteed to be availble.
We were lucky to snag their last speed boat available since we didn't have a reservation. Our group of 9 fit well on the quick boat, and after an hour or so of paperwork and prep, we were underway for our half day (5 hour) adventure.
I use a variety of mapping apps when on an adventure, and for this one I used the trusty Topo Maps for iOS. I downloaded the high-resolution USGS 7.5' Topo layers for the area, and was able to easily figure out our location within the canyons.
Our first stop was, of course, Antelope Canyon via Lake Powell. Although we saw quite a few other boats, and even a couple of kayaks, it wasn't terribly busy. We were able to make it quite a way up the canyon before it became too narrow to continue with the speed boat.
We enjoyed a nice lunch while underway out of Antelope, then headed back north, then east, toward Navajo Canyon.
Completing the entire length of Navajo Canyon can take several hours, even in the quickest watercraft, so that was never part of our plan. Instead, we explored the first 2/3 or so of it's length before deciding to pull the boat onto a beach for a little relaxation. The kids had a great time getting filthy in the sand, while the adults enjoyed the views and discussing what the area must have been like before the flood.
With just over two hours of boat time left, we decided to push off the beach and do a little more exploring. Unfortunately the boat had become beached to the point that it took four of us about 20 minutes to spin it around and get un-stuck. Luckily we still had time to get out of Navajo Canyon and make our way north a bit more.
We pushed just over the Utah border and very near the largest part of Lake Powell, and were able to get a glimpse of the vastness of this place. Clearly one could spend weeks exploring all the canyons and never see the same place twice.
With just under an hour left, Andy pointed the speedboat south and we buckled in for a fast (and bumpy) ride back to the marina. Upon our return and after gassing up the boat, we made it back to dry land. We were lucky to find a cart-shuttle with a trailer attached, so all 9 of us + gear got a nice ride up the hill.
Even if you can only explore the water for one day, it's definitely worth renting a boat or kayak and finding adventure out on the lake. You're sure to see things that few others get to enjoy.