The Weerribben holds one of the most diverse wetland wildlife assemblages in the Netherlands. The reed beds support breeding populations of great bittern, marsh harrier, and bearded reedling — species that require extensive undisturbed reed for nesting and are genuinely rare elsewhere in northwest Europe. Eurasian otters, reintroduced in 2002 after a long absence, are now firmly established and most active at dawn and dusk near the water channels.
The butterfly fauna is exceptional. The large copper, chequered skipper, and several fritillary species breed in the meadow and fen habitats that border the reed. In summer the park is also rich in dragonflies, including species that require unpolluted, vegetation-rich water. The combination of habitats — open water, reed, fen meadow, and carr woodland — means that species diversity is unusually high for a relatively small area.
For bird watching, the best positions are the elevated observation hides at the levee ends, which allow views over open reed beds without disturbing nesting birds. Early morning is most productive; the bittern's booming call is most often heard at dawn from late March through June.