Bronx Zoo - Congo Gorilla Forest

Hotgrass is amazing in exhibits, as at first glance it is often overlooked and it is only after a minute or two that it becomes obvious. If I had to choose between hotgrass (which is used in many major American zoos) or an ugly fence or wall then the hotgrass would be my choice every single time. It is a thousand times more effective than any solid, much larger type of construction such as barbed-wire or chainlink fencing.

Here is a photo from a bit further back:

http://www.zoochat.com/547/bronx-zoo-congo-gorilla-forest-41163/

I imagine it'd be pretty useless as a primary barrier though, seems pretty flimsy. It's probably best used for covering plants and keeping animals off trees and the like. It's used a lot in Gorilla kingdom at London.

I know of no instance where it is used as a primary barrier.
In this pictured exhibit, the primary barrier is a dry moat. The hot grass is merely to keep the okapi out of it and on exhibit.

When hotgrass is used "on the ground" and properly planted out, and painted, it is less visible. When the tall version is used, as in this picture, it doesn't resemble anything natural and so is more obvious.

Is there a reason to keep the animals out of the moat other than keeping them on view? Why not allow the animals access to it and increase the area available to them?

I think it is safe to say that in general, in North American zoos, keeping animals on view is important. A top visitor complaint about zoos is that the animals can't be seen. It would be better for animals to have "privacy space" within the exhibit than down in the moat where not even keepers can observe them. One runs the risk that they will prefer the moat space to the exhibit and never be seen...which doesn't help the zoo teach conservation, biology, etc. OR pay the bills. When animal enclosures are planned, it is expected that the "on view" area will offer more than adequate space for the animal(s). The moats are not quality animal space anyway...they are designed to hide a wall only and often lack space for comfortable maneuvering, resting, etc.

(In this exhibit, an okapi can retreat to the far back, quite a distance from people, and it will be next to impossible to see it)

i do know Chester does use this on the new otter/babirusa enclosure to stop the otters begging

Where are they then?

hotgrass is where the windows are