I&#x27;d place beacons in live fish. They are well suited to navigating underwater hazards.<p>Acoustically ping a serial number for a couple of days. Place an array of sonobuoys in the likely outlet area, scan with boats further afield. If there is a fish sized outlet, then they should be able to get out. If you start finding your fish you can start refining the resolution of the search and plopping more fish in the falls.<p>At the same time, lower teathered hydrophones into the falls at various distances. If the pingers accumulate somewhere there, then you have a suggesting of fish impermeable structure.<p>I might need to add lights to the fish so they can see.<p>Plus you&#x27;d get some great YouTube footage a fisherman who catches a fish with headlights.