 The greater lock is against the general south (right, towpath or Surrey) bank of the river which is for 500 m north-east here; a middle lock being that most regularly used spans a long thin island which has lawns, places for boat owners to sit and a lock keeper's cabin and short thin island which is a thin wedge of concrete and a broad canoe/kayak stepped portage facility.The river downstream of the lock is the Richmond and Twickenham reach of the Tideway, a reach of semi-tidal river due to the fact the Richmond Lock and half-tide barrages limits the fall of water thereby maintaining a head of water to aid navigability at and around low tide.Though the weir at Teddington Weir marks the managed river's usual tidal limit, after prolonged rainfall causing very high fluvial flow, specifically at high tide, a higher limit of slack water (stand of the tide) causes eddies to arise as far upstream as the top of this reach, the next lock.