Five porpoises spotted in River Thames They later added: "They are surfacing regularly and are staying in the Westminster area." The mammals usually travel and look for fish in small schools and break the surface of the water as they swim. The Marine Conservation Society said the sighting of them in the Thames was rare. A spokesman said: "It is unusual for five animals to be in the river as porpoises tend to be seen alone, and in smaller groups. It isn't possible to say whether the tidal surge is the cause of the porpoises being in the river, but it could well be related, either to the tidal movement, or as a response to the particularly rough seas beforehand. The outer Thames Estuary would have been relatively sheltered from northerly offshore winds. The pod should should be able to navigate back to sea, through Thames barrier when tide goes out and barriers are opened.