Do NOT keep dendrobatids (and other terrestrial frogs, such as toadlets, mantellas, and harlequin toads) in an enclosure with any sort of water feature. They can and will drown; despite what many say, even dart frogs that are somewhat good at swimming (e.g. Epipedobates) will quickly tire if the body of water is relatively large (and if it can support fish, it probably is) and drown. I lost my second Ranitomeya summersi male because a springtail culture cup filled up ~1/2 of an inch after a misting system failure and the frog was unable to escape (that individual had some trouble eating beforehand, which may have also had something to do with it). Dart frogs are best kept in a species-only terrestrial enclosure; if this is something that sounds unappealing, there are several species of semi-aquatic frogs or some arboreal frog species that may do well with a water feature.