The Louisiana Waterthrush is very similar to the Northern Waterthrush, but there are some differences.
The chest and belly of the Northern Waterthrush are more washed yellow and are more densely streaked, whereas the Louisiana Waterthrush has more white underparts and less dark streaks.
In addition, the Louisiana Waterthrush has a heavier bill and a nearly pure white eyebrow, while the Northern Waterthrush's eyebrow is usually somewhat buffy.
The eyebrow of the Louisiana Waterthrush is wider at the rear.
Perhaps the most diagnostic morphological feature is the throat, which is streaked in the Northern Waterthrush but plain in the Louisiana Waterthrush (clearly visible on the photo).

Visiting a zoo on a birding trip may be a little strange and "artificial" but the Belize Zoo is actually a great place to see wild birds (and other wild animals) in the surrounding forest.
The Belize Zoo is settled upon 29 acres of tropical savannah and exhibits over 125 animals which are all native to Belize. 
The zoo keeps animals which were either orphaned, born at the zoo, rehabilitated animals, or sent to the Belize Zoo as gifts from other zoological institutions.
In addition to seeing and learning about Belizean wildlife, the zoo is a good spot to see wild birds like Common Tody Flycatcher, Rufous-browed Peppershrike, Bronzed Cowbird, Red-capped Manakin, Blue-gray, Yellow-winged, and Hepatic Tanagers, Tropical Pewee, Yellow-throated Euphonia, Grace's and Hooded Warblers, Worm-eating Warbler, Plain Chachalaca and Green-backed Sparrow.

Belize Zoo, Belize, 5 March 2009