Spotting a marine mammal

What to do if you spot a marine mammal

 Marine mammals are regularly spotted in the Tidal Thames by members of the public. Here we provide advice on: 

  • What behaviour you can expect to see from these mammals
  • Who you can report sightings to and what will happen when you report a sighting.

We also provide advice on why you should keep your distance from them and list links to more detailed information. This information is summarised on a leaflet available here

A group of seals seen on the 2017 Thames Seal Survey

Natural Behaviour / Normal to see


  • Haul-out onto the foreshore, pontoons, sandbanks to rest, sleep, digest food and when moulting
  • Swimming and diving 
  • Banana shape – mostly for harbour seals
  • Wet patches around their eyes
  • Red / bronze coloured fur from iron ore

Porpoises and dolphins

  • Individual in the water
  • Swimming breaching, porpoising, tail / head slapping

You can report your sightings for collation in our marine mammal sightings map.  

Harbour seal

Behaviour that could indicate injury or illness


  • Individual showing signs of an injury in the water or foreshore
  • Observable skin lesions
  • Individual tangled in net or plastic
  • Individual showing signs of malnutrition (i.e.: concave flanks, indented stomachs)
  • Individuals showing signs of laboured breathing (could be a sign of Phocine distemper virus)

Porpoises and dolphins

  • Individual on the foreshore
  • Individuals far upstream in the river
  • Floating (not actively swimming)
  • Individual showing signs of an injury
  • Individual tangled in net or plastic

Based on the information above, if you think the animal may be injured, ill or in distress, please phone 0208 855 0315 (24 hours).  This will take you through to the Vessel Traffic Services of the Port of London Authority (PLA).  They will send a nearby vessel to investigate and will coordinate an emergency response if necessary. The emergency response will be by British Divers Marine Life Rescue (BDMLR) or the RSPCA and may involve support from the Metropolitan Police marine unit, the London Fire Brigade river unit, the RNLI or the PLA. If the animal is sadly dead the Cetacean Stranding Investigation Programme will be called.

Seals in the Thames

How you should behave around marine mammals 

Please appreciate these intriguing animals from a distance. If you get too close you may cause them distress, or to panic and bite. When hauled out onto land or a pontoon seals can feel vulnerable and be easily startled. Noise and being approached by people, boats, kayaks or dogs etc. can cause seals to panic and move back into the water – this can cause them injury and exhaustion.

Please do not attempt to rescue a mammal.  You may harm the animal or you may be harmed in the process. Also be aware that the Thames is a tidal river (as far as Teddington) with a tidal range of up to 7m.  Waves from passing vessels can catch you unawares and the river has very strong and fast currents.  

If you see a marine mammal in the water, many of the same rules apply. Please do not surround the animal with large numbers of people/watercraft and never approach marine mammals head on so that the animal has room to escape. Approach the marine mammals at low speeds and remain more than 100 metres away, avoiding driving through groups, never attempt to feed them and give mothers and calves extra room. 

A group of seals seen during our aerial surveys in the Greater Thames estuary

ZSL has an easy Code of Conduct to follow if you see marine mammals in the Thames.

Information for responsible wildlife watching operators is available here

If you are worried about any wildlife crime, -the police have Wildlife Crime Officers that can deal with cases of crime against wildlife, including the killing, injuring and intentional or excessive disturbance to them.  If you witness an incident then call the Police incident phone number (101) for advice and assistance or check out the wildlife crime website

Tidal Thames Marine Mammal Partnership

This page has been produced by the Tidal Thames Marine Mammal Partnership which is a coalition of first responders, wildlife organisations and the harbour authority which aims to raise awareness of how to act around marine mammals in the Thames.  The partners are :