Calstock slipway

Calstock Viaduct crosses immediately overhead, a Grade II*-listed railway bridge about 37 metres high, completed in 1908 from 11,148 precast concrete blocks cast on site. Twelve 18-metre arches and a smaller arch carry the line across the river on tapered piers, three of which stand in the water.

Upstream the tidal reach continues several miles to Gunnislake Weir, a rock apron with two fish ladders around two metres high spanning the full width of the river, which marks the limit of navigation. Downstream the channel winds past Cotehele, Weir Quay, Pentillie and Cargreen before opening into the Hamoaze; the best water lies on the outside of the bends, and the foreshore dries to mud at low-water springs.

The reach lies within the Tamar Valley National Landscape and the Plymouth Sound and Estuaries Marine Protected Area, and forms part of the Tamar-Tavy Estuary Site of Special Scientific Interest, which runs from the Tamar Bridge to Gunnislake Weir and protects saltmarsh, reedbeds and mudflats used by wintering wildfowl and waders. The upper Tamar holds the only known allis shad spawning population in the UK. In November 2021 the Environment Agency breached the old flood bank at Calstock to create 11 hectares of new intertidal habitat as part of a flood-defence scheme.