The Port of Exeter extends from Blackaller weir in the heart of the City to the safe water mark a mile or so out at sea off Exmouth .  Exeter City Council is responsible for marking a navigation channel from the sea to just above Topsham. The Port area is subject to a maximum speed limit of 10 knots in the estuary and off shore.  From time to time Local Notices to Mariners (Local NTM) are issued to alert water users of any activities which may affect their passage in the river and the estuary.