Complex sentence: A weir connected the navigation to the tidal river Blackwater at Heybridge, where it powered a water mill. Heybridge mill was demolished after severe flooding in this area in 1953, but the mill house still stands.
Split into simpler sentences: A weir connected the navigation to the tidal river Blackwater at Heybridge. Water flowing over this weir powered a water mill. Heybridge mill was demolished after severe flooding in this area in 1953, but the mill house still stands.