I'm actually trying to create an alien ecosystem, so changing orbits, what's exhibiting tidal forces and the geography and such is welcome if needed. I also wonder how stable a setup with dramatic tides (flowing into an otherwise stagnant area) would be. The point of this specific ecosystem on my planet is the evolution of the dominant race; they evolved in fertile swamps that had dramatic tides. The high tide would be about 7 or 6 feet deep or so (essentially tall enough for a human to swim in), and the low tide would be knee/ankle deep, with days where there's almost no water at all. Anyway, it would need to be stable enough for a species to evolve and adapt to it.
BONUS: It would be helpful to know how this setup could develop, too, but that information is not necessary. I really only need to know if it is possible and stable.