0:00:39 > 0:00:43Strangford Lough is a vast inland sea -
0:00:43 > 0:00:46the largest saltwater lough in the United Kingdom,
0:00:46 > 0:00:51with 120 islands and 150 miles of its own twisting coastline.
0:00:51 > 0:00:54This huge body of water is tidal,
0:00:54 > 0:00:57connected to the sea by a narrow channel.
0:00:57 > 0:01:01Twice a day, fierce currents surge through this bottleneck.
0:01:01 > 0:01:04The tide's pouring in from the open sea,
0:01:04 > 0:01:07and you can feel it trying to push the ferry into the lough.
0:01:11 > 0:01:15The tidal torrent is the life blood of this exceptional environment.
0:01:15 > 0:01:16The World Wildlife Fund
0:01:16 > 0:01:20say Strangford is one of the most important wild places in Europe.
0:01:20 > 0:01:24And no wonder. There are over 2,000 marine species here -
0:01:24 > 0:01:27that's three-quarters of all the plants and animals
0:01:27 > 0:01:29found in Northern Ireland.
0:01:29 > 0:01:31For our zoologist, Miranda Krestovnikoff,
0:01:31 > 0:01:33the fierce currents in the lough
0:01:33 > 0:01:36will make Strangford a very difficult dive.
0:01:36 > 0:01:39350 million cubic metres of sea water
0:01:39 > 0:01:42flood though the lough every tide.
0:01:42 > 0:01:45This twice-daily pulse of water is a living soup.
0:01:45 > 0:01:48It's packed full of microscopic life
0:01:48 > 0:01:51that fuels the food chain in the lough.
0:01:51 > 0:01:55Surging water also makes life difficult in the deep.
0:01:58 > 0:02:00Wait!
0:02:01 > 0:02:03The current just takes you.
0:02:03 > 0:02:07This current's moving too fast!
0:02:07 > 0:02:10I'm going to try and get out of the current a bit,
0:02:10 > 0:02:12and have a closer look at the marine life.
0:02:19 > 0:02:23We've got fairly bad visibility.
0:02:23 > 0:02:27That green colour is a bloom of plankton.
0:02:27 > 0:02:29That's good news for the animals,
0:02:29 > 0:02:32because that's the food they feed on.
0:02:32 > 0:02:35You can just see between the timbers of this old wreck,
0:02:35 > 0:02:40a beautiful conger eel, really blue with big eyes.
0:02:40 > 0:02:43It's a big fish and the only way it can really survive
0:02:43 > 0:02:47is by hiding and waiting for food to come to it.
0:02:50 > 0:02:53Its rich marine life makes Strangford Lough
0:02:53 > 0:02:54ripe for exploitation.
0:02:54 > 0:02:57Dredging for scallops and prawns
0:02:57 > 0:03:00has already destroyed miles of the seabed.
0:03:00 > 0:03:05The bottom is scraped bare, leaving a lifeless underwater desert.
0:03:05 > 0:03:07Though dredging is currently banned,
0:03:07 > 0:03:09the commercial pressure is unrelenting,
0:03:09 > 0:03:13and it might be permitted again if the environment recovers.
0:03:19 > 0:03:24Strangford Lough is a fragile ecosystem, despite its size.
0:03:24 > 0:03:27It stretches inland for 20 miles.
0:03:27 > 0:03:30Here it changes into a placid, shallow sea.
0:03:30 > 0:03:36The falling tide reveals enormous mudflats, literally full of life.
0:03:36 > 0:03:40You can see the worm casts and a few shells and cockles on the surface,
0:03:40 > 0:03:43but I guess there's more...down?
0:03:43 > 0:03:47Yes, definitely. We have got loads of life in the mudflats themselves.
0:03:47 > 0:03:51- If we take a chunk out and see what is in there.- Look at that!
0:03:51 > 0:03:54There is a fantastic bloodworm burrow there.
0:03:54 > 0:03:57There's a ragworm.
0:03:57 > 0:03:59There's quite a lot moving as well.
0:03:59 > 0:04:01You can see it is teeming with life,
0:04:01 > 0:04:05and this is what supports all of the different species of birds.
0:04:07 > 0:04:12Over 70,000 birds come here every winter for the rich pickings.
0:04:17 > 0:04:19Belfast is only 12 miles away,
0:04:19 > 0:04:24with its commuters hungry for housing in such a lovely setting.
0:04:24 > 0:04:27The threat of pollution from overdevelopment
0:04:27 > 0:04:28hangs over the whole lough.
0:04:28 > 0:04:32In an ideal world, what would you like to change for the future?
0:04:32 > 0:04:34It would be great if Strangford Lough
0:04:34 > 0:04:36was made a Marine National Park,
0:04:36 > 0:04:39because we don't have any yet in the UK and if it was one of the first,
0:04:39 > 0:04:41that would be fantastic
0:04:41 > 0:04:43but it would also raise awareness of how special it is
0:04:43 > 0:04:46and it is a place that needs to be protected really well.
0:04:59 > 0:05:02Subtitles by Red Bee Media Ltd