Around the world, many fishways have been constructed to provide a route for upstream migrating fish to pass dams.  Most were designed for salmon, but other species have also been targeted.  While sometimes successful, often these fishways are not, because they were constructed with insufficient hydraulic and biological knowledge about the target species, or were installed in locations or with insufficient attraction flow for them to be effective.  The hydraulics of several fishway types have been well studied, but they lack sufficient biological knowledge for how many species will respond to the hydraulics within them.  Not surprisingly, in some of these fishways some species can successfully pass, but some species cannot.  Results of evaluations indicate that when sufficient hydraulic and biological knowledge exists for a species, it is possible to construct successful fishways.  This requires knowing how behaviour and swimming abilities interact with hydraulic conditions in different fishway configurations. This type of information is crucial to the development of fishways that have the best chance of being effective.  There are different ways to monitor fish movements and evaluate fishway effectiveness, using fairly simple to fairly sophisticated methods.  Fishway evaluations have evolved as animal tracking technology developed, from simple observations on fish numbers, to state-of-the-art physiological measures, including heart rate and stress level.  Although it is not always feasible to use the latest technology, scientific assessment information is needed for many species, as fishway science continues to advance to hopefully one day create fishways that all species can successfully pass.