here's some interesting information about the Belize River I thought I'd add so that its search-discoverable...

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Don't know of any printed source for this info, but the Belize River has a
bar at the mouth of less than 3 ft, 2 ft in December low tides. The
dredged channel silted in in less than one year, the natural channel is
still the deeper one. Head room at the Haulover Bridge is about 9 ft.
From just inside the river mouth the water depth varies from 8 ft to 45 ft
in some holes, with an average of 12-14 feet up to Double Run. From DR
upriver in the dry season there are some rocks breaking the surface in some
places and many just under the surface, not navigable even with outboards
unless one has experience reading the water or a good local river resident
for guide. Just up from Grace Bank there are navigable rapids in many
places, but not for the casual boatman. At Little Falls the rocks and
channels are obvious but mist be navigated with great care. Above Black
Creek and before May Pen there are rocks showing in the dry season, but
completely out of sight in the rainy season. From May Pen to Bermudian
landing the river is easily read after the practice of getting there.
After Bermudian Landing I am not familiar with the river. During the Ruta
Maya and Extreme Canoe races Mike Green of Chaa Creek has run the rescue
boat from Cayo to Belize City.