Straddling one of the busiest cities in Europe is a wildlife oasis.
Here birds, not humans, are the masters.
During the winter months, there can be as many as 40,000 of them nesting, crowing and soaring through the skies.
This vast expanse of water and islands does not have the majestic ships you see in Portsmouth Harbour, or the lavish yachts that frequent Chichester Harbour, but many will agree it is one of the most tranquil harbours in England.
It is, of course, Langstone Harbour and today I am being treated to a tour of all its wonders.
Every year committee members from the Langstone Harbour Board, together with other interested parties, take an inspection of the harbour to see how it is faring.
It’s an overcast summer day and the rippling water looks murky and mysterious.
Despite not having the ‘Area of Outstanding Natural Beauty’ designation of its neighbouring harbour to the east, the views across to the South Downs and the leafy vista of Hayling Island are a splendid sight.
As we board the chugging boat at Hayling Island, there’s a quiet excitement about what awaits.
Louise MacCallum, who is the environment officer for Langstone Harbour, says: ‘It’s really nice for the board members and stakeholders to get out on the water.
‘It’s important they get a real feel on the ground for what the harbour authority does.
‘Many people see Langstone Harbour from the shoreline, but you get a much better perspective of the harbour on the water, especially when you get into the middle of the harbour with Hayling Island on one side and Portsmouth and Spinnaker Tower on another and you can see Farlington Marshes and the commercial port.
‘Anybody who comes to Langstone Harbour will be able to see internationally-important wildlife.’
As the boat glides into the heart of the harbour, I get a true sense for how big and diverse these waters are.
There are the concrete remnants of the Mulberry Harbour, a poignant reminder of Hayling Island’s role in the D-Day landings.
Further north are islands with colonies of Mediterranean Gulls, Black-headed Gulls, Common Terns, Sandwich Terns and the rare Little Tern, so I am told.
The grassy greenery of Farlington Marshes dominates the view at the north of the harbour, while our boat is dwarfed by the colossal tankers that are fetching aggregates to the two wharfs.
To the north east are the rusty ruins of the old Hayling Billy bridge.
The salty, fresh breeze is exhilarating.
And in the middle of the harbour is surely the best barbecue spot in the city.
This floating platform is used by the water skiing club for their summer get-togethers.
Louise laughs: ‘Every time I am here, I think of chilling out with a beer and a burger.
‘But I would have to learn to water ski! Maybe it would be worth it.’
The boat-goers are ready with their binoculars and cameras, keen to capture the moment a tern dives into the water to catch a fish.
Councillor Gerald Shimbart, a retired tailor who made uniforms for Royal Navy top brass, says: ‘It’s a wonderful resource – it’s got a bit of everything.
‘You have got lots of birds, lots of fish, seals and all sorts of things for people to look at and enjoy.
‘It’s a lovely feeling being on the water – it’s so natural and open. I just love it. I don’t get enough of it.’
Cllr Jackie Branson, a retired teacher from Warblington, says: ‘It’s a beautiful asset.
‘I think it’s very under-rated.
‘You can go and see the birds nesting up at the oysterbeds.
‘I think it could increase its leisure interest, but of course Chichester has more scenic value.
‘My favourite part is the oysterbeds – it’s just a lovely walk near the Hayling Billy Trail. It’s a hidden gem.’
The Lord of Mayor of Portsmouth, Councillor Frank Jonas, says: ‘My first introduction to the harbour was 64 years ago when I was five.
‘My uncles always had fishing boats.
‘My son is now carrying on the tradition. I like going out on the boats, but I wouldn’t call myself a fisherman. It’s a wonderful harbour for recreation, although underused.’
Every now and then, the Tannoy comes on with snippets of interesting information.
Alas, today, because we are at high tide, we are unlikely to see any seals, says Louise.
The last survey counted six seals in Langstone Harbour, with 16 in adjoining Chichester Harbour.
Louise says: ‘The good news is we have more species of seals in Langstone than they do in Chichester because we have both grey seals and harbour seals.’
The largest animal to enter the harbour in recent years was probably a six-tonne 26ft Northern Bottlenose whale that unfortunately beached itself on one of the mudflats.
Recently, Louise spotted a giant sunfish – which can grow up to 10ft in length and weight up to 2,200lbs – near the entrance to the harbour.
The most recent visitors are an army of jellyfish.
‘For whatever reason, there are thousands of them swimming around the south coast at the moment,’ says Louise.
‘They are a pale bluish colour and can get as big as a dustbin lid.’
Cllr Ken Smith, on the harbour board for 12 years, remembers moves to build a big marina and hotel at Broadmarsh.
He said: ‘I have seen it go from a rather haphazardly-run harbour to a really efficient harbour.
‘We have seen projects come and go.
‘We have two objectives – to keep the harbour nice and protected, but also developing it for tourism.’
He tells me his favourite spot is Farlington Marshes, with its views of the bird sanctuaries.
Cllr Lee Mason, chairman of the Langstone Harbour Board committee, says: ‘It’s an amazing resource when we have a city like Portsmouth with such a high population.
‘I wish more people would take an interest in it.
‘Someone the other day got a photo of a seal and they were amazed. We have a whole family of them in Langstone Harbour.’
As we head back to dry land, there’s contentment on everyone’s faces.
The serenity of the harbour, free of any of vrumming cars, is clearly a de-stressing experience for many.
Louise admits she has the ‘best job on the planet’.
She says: ‘I think how lucky I am to live in Southsea. I get to live in an amazing city, but five minutes away I can come to this really important space for wildlife.’
Jackie Branson, who is still dreaming of living in a home with an unspoilt view of the harbour, is determined that this beauty spot should remain beautiful.
She says: ‘This harbour will still be here long after we are gone, so we have to make sure it is protected for future generations.’
The job of Wez Smith is to look after RSPB bird sanctuaries in the north of the harbour.
The 34-year-old, who moved back to ‘civilisation’ as he says after living out on small islands off the coast of Scotland, says: ‘I have only known it three years but it’s an absolute gem on the south coast of England.
‘We have got one of biggest seabird breeding colonies here.
‘It’s just a short distance away from Portsmouth - one of the most densely-packed cities in Europe.
‘It’s fascinating, quite frankly, the fact this site is here, so close to so many people.
‘You have birds that come 6,000 miles to this site every single year to breed their young and raise them.’
The Little Tern is his favourite animal in the harbour ‘because there are so few of them’, he says, adding: ‘It’s nice to get back to a place where there are people, as well as wildlife.’
The harbour is the ideal place to canoe and kayak.
Joe Chamberlain, 52, from Portsmouth Canoe Club, says: ‘We use the harbour for training every Monday night by the harbour entrance.
‘It’s a good spot.
‘It gives us a good variety of water - we can go out into the sea and get some rough water and we can come into the harbour and have calm areas for novices.
‘We sometimes do tours around the harbour and enjoy the wildlife around the islands.
‘It’s a peaceful place compared with the busy Portsmouth Harbour.
‘Even Chichester Harbour is quite busy, so this is a tranquil place to retreat to.
‘It can get quite lively on the harbour entrance when you have a strong spring ebb against a southerly wind.
‘Sometimes it gets a bit too much.’
At a glance
The Langstone Ark is a project which aims to collect images of all the flora and fauna associated with Langstone Harbour. Anyone can contribute to the project by e-mailing a photograph to firstname.lastname@example.org
There are opportunities for a variety of activities in the harbour at Portsmouth Watersports Centre, off Eastern Road. Visit portsmouthwatersports.com or call 023 9266 3873.
The Hayling Billy Trail is a great way for all the family to see the harbour. The walk or cycle starts at The Spring, in East Street, Havant.
For more information on the work of the harbour board, visit langstoneharbour.org.uk.