<Tr> <Td> Swanscombe Marshes / Broadness Lighthouse, Swanscombe </Td> <Td> <Table> <Tr> <Td> </Td> </Tr> </Table> </Td> <Td_colspan="2"> Grays (or, more rarely, Grays Thurrock) </Td> </Tr> <Table> <Tr> <Td> </Td> </Tr> </Table> <Tr> <Td> Northfleet </Td> <Td> <Table> <Tr> <Td> </Td> </Tr> </Table> </Td> <Td_colspan="2"> Tilbury, West Tilbury </Td> </Tr> <Table> <Tr> <Td> </Td> </Tr> </Table>

Is the river thames fresh or salt water