Castor Weir Wave is a fickle little feature on the River Nene near Peterborough, England, formed by the drop over an old river weir. It's mostly a kayaker's wave, but it is surfable when conditions line up, and locals who know the weir keep closer tabs on it than any posted gauge does. Hard data on seasonality is thin here—this one runs on local knowledge more than online flow charts, so it pays to ask around before making the trip. Treat it as a bonus session if you're already paddling the Nene, not a destination wave on its own.