Imagine the entire population of Australia moving to a city the size of Canberra. That kind of population explosion is what the Nigerian city of Lagos is now preparing for. As one of the world's fastest-growing mega cities, Lagos is being hailed as an investment Mecca, even drawing former US president Bill Clinton to sing its praises. So, how is the city managing such extraordinary growth, and is everyone there happy with the way it's going? Dateline's Yaara Bou Melhem travelled to Lagos to find out.

REPORTER: Yaara Bou Melhem

This is Lagos in the not too distance future.

DR OBAFEMI HAMZAT, LAGOS STATE COMMISSIONER FOR WORKS AND INFRASTRUCTURE:  In terms of return on investment, I don't know if any other place is better than Lagos now.

DAVID FRAME, EKO ATLANTIC MANAGING DIRECTOR:   Lagos will become the financial hub for the continent of Africa.

But this vision is a world apart from this Lagos that millions know today.

CHIEF FRANCIS:  We can't go to any other place. We are fishermen, we are water-bound.

With a rapidly expanding economy and a lucrative oil industry, Lagos is booming. Nigerians and foreign investors alike are converging on Lagos in search of new opportunity.

TAOFICK OKOYA:  I believe that we've only just scratched the surface.

Taofick Okoya is an entrepreneur. He's found a niche market - selling dolls that celebrate Nigerian culture - but says Lagos offers opportunity across all sectors.

TAOFICK OKOYA:  We are still Third World and striving really fast to become a mega city, and even Nigeria as a country, as a whole - there are so many opportunities in terms of technology, infrastructure. Ohhh - it's going to be a huge boom.

The centrepiece of the booming new Lagos is this audacious, privately funded project to build a brand new city that quite literally rises from the Atlantic.

DAVID FRAME:  Eko Atlantic, in total, is 10 square kilometres. We project 250,000 permanent residents, and a further 150,000 who will be communicating on a daily basis. 10 square kilometres is not a small area. It's bigger than most towns.

Eko Atlantic is reclaiming thousands of acres of land lost to sea erosion by building on sand dredged from the ocean floor.

DAVID FRAME:  The main city, all the infrastructure, the roads, the utility services, and everything that goes to make the footprint of the city will be completed by the end of 2019.

Land is a very valuable commodity in Lagos, and this multibillion-dollar project will have approximately 7 million square metres of it to sell.  And they're selling it hard.

VOICEOVER:  The evolution of Eko Atlantic will change the face of Lagos, and open a new gateway to your success in Africa.

DAVID FRAME:   It's a city being developed with no financial burden on government whatsoever. We provide and maintain all the services you would normally expect from a city.

Not surprisingly, this is very appealing to the state government.

BABATUNDE FASHOLA, LAGOS STATE GOVERNOR:  Although it is not finished, this is already a success story. The road that was lost to the sea is back, and more buildings are springing up in the anticipation of the opportunities that lie ahead.

BILL CLINTON, FORMER US PRESIDENT:  They have reclaimed 5 million square metres of land from the sea.  They have built the beginnings of this amazing wall - an ingenious engineering feat.

This is what former US president Bill Clinton is referring to - the so-called Great Wall of Lagos. A barrier 8.5km long that Eko Atlantic claims will prevent coastal erosion and keep the affluent Victoria Island safe from flooding and climate-related events.  Situated on the Atlantic Ocean, Lagos has long been at the mercy of the sea, and climate change is raising the stakes.

DR OBAFEMI HAMZAT:   On the average, we are 2m below sea level. So when it rains, naturally it will flood, because we are below water. As such, the essence of building a road is not to move people along, but also to move water. And to be able to move that humungous mass of people in a manageable way - that would be the aim for Lagos going forward.

But Eko Atlantic's solution to these challenges has come in for scathing criticism. An article in The Guardian claims the development will bring "climate apartheid".

DR OBAFEMI HAMZAT:  I think it's outrageous. Honestly, it's intellectually shallow. The reality is, if you don't have it - I just said that - if you don't have it, the whole of Victoria Island could disappear. Do we allow it to disappear - no!  There are companies there, there are residents there, there is economic activity of the state here. I don't see that at all.

And David Frame is unapologetic about Eko Atlantic's elite target market.

DAVID FRAME:   Well, yes, we can call them elite. We can call them the rich, the wealthy - whatever. But the real market, as we see it, is for that middle-management middle class. We want to cater for that group of people, because they are in large numbers.

Notwithstanding Lagos's burgeoning middle class, Taofick Okoya prefers to cater to low-income earners.

TAOFICK OKOYA:  We're targeting that market, which makes up of the majority of the - well, majority of the population.

REPORTER:  Would that have been possible, say, 10 years ago? Or is it only possible now with the boom?

TAOFICK OKOYA:  Would it have been possible 10 years ago? Um, no, I don't think so.

Just 15km away is Makoko - a bustling aquatic slumb that is home to an estimated 250,000 people. Almost everything in this traditional fishing community is done on the water.

CHIEF FRANCIS:  They are waiting for fishermen to come back for them to buy fish.

Makoko Chief Francis is showing me around his community.

CHIEF FRANCIS:  It's a fishing community. We have a timber industry, as we go now you will be seeing logs.. so millers place where they saw the planks for constructing of our structures on water.

It's often called the Venice of Africa, but there are stark differences. Makoko is poor, overcrowded, and largely without government services. This is how you get around Lagos's oldest and largest slum, Makoko. It's been inhabited for about 150 years, but there's still a lot of infrastructure problems.

It may be on the water that access to clean water, sewerage and waste disposal are major issues, leading to disease and health problems in the cramped population. Life  expectancy here is under 40.

CHIEF FRANCIS:  We need government to improve this community. Government hospital is not here. School is not here, government should provide all those things for us. And the water, no government water. That is why you can see boreholes everywhere. If we don't have boreholes we can't save drinking water or bathing water or do anything.

The most innovative proposal to address Makoko's problems has come not from the government, but from a Nigerian architect with funding from the United Nations. This award-winning floating structure is a school. It's immune to variable water levels, it harnesses rainwater on its sloping roof, and it provides renewable energy through solar panels. It could serve as a prototype for entire floating communities. But Chief Francis says there's no political will to bring sustainable development to Makoko.

CHIEF FRANCIS:   We are Lagosians also, we are part of it. So government should reconsider us as human beings and help us for improvements of this community.

Residents say Makoko has been declared illegal, and they live in fear of eviction. Indeed, in 2012, 500 homes were destroyed by men with chainsaws in a government-ordered demolition.

CHIEF FRANCIS:  This place was filled up with houses before. They started down there, you can see some marks there. All this place was filled with houses, all were demolished.

The Lagos State Commissioner for Works, Obafemi Hamzat, denies that the community was ever declared illegal.

DR OBAFEMI HAMZAT:   Illegal? No. No.

REPORTER:  That's the basis for the demolitions that happened two years ago?

DR OBAFEMI HAMZAT:   Well, no. You see, remember, even in any society, there are demolitions that happen. In in order to build, you need a permit, like anywhere around the world. Makoko is not going to disappear - it's going to be there. But can it be better? Yes, I think the answer is yes. Every city goes through a regeneration. Every city. In the process of regenerating, a lot of things have to change. So, change is constant.

Chief Francis and the other Makoko chiefs are suspicious of the government's plans, and have sought the help of a local NGO.

EMMANUEL NWAGHODOH, SOCIAL AND ECONOMIC RIGHTS ACTION CERTRE:  We are talking about what the government wants to do with us and how we feel about it.. What do you think the government wants to do?

CHIEF FRANCIS:  The government wants to rehabilitate it, want to sandfill it and sell it to the rich people.

Chief Francis is speaking with Emmanuel Nwaghodoh,  of the Social and Economic Rights Action Centre or SERAC, a community group that advocates for slum settlements like Makoko. SERAC has succeeded in getting a court stay against former demolitions, and is now working with residents on a regeneration plan.

EMMANUEL NWAGHODOH:  Our plan is redeveloping Makoko where it is, leaving the traditional setting for the outside world to come in and see. Retain its traditional mood, and redevelop it in such a way that it becomes attractive to the outside world.

Lagos's population is expected to almost double within the next decade, making it one of the world's most populous cities.  Such rapid urbanisation poses serious infrastructure challenges - not just in terms of housing and people movement, but also managing a growing waste-disposal crisis.

In the 1980s, Nigeria's military rulers decreed the morning of the last Saturday of every month Sanitation Day. In Lagos, the authorities take it very seriously.

DR TAOFEEK FOLAMI:  Essentially this is what we are trying to ensure that people actually comply with some basic simple rules in terms of their waste disposal.

I'm with Dr Taofeek Folami, the special adviser to Lagos's ministry of environment. He's invited me along for a Sanitation Day tour.

DR TAOFEEK FOLAMI:  We are going to see the first place on the itinerary, it's a drainage channel, specifically we are going to look at the challenges they are facing here.  We want to see people keeping their frontages clean.

Lagos produces up to 10,000 metric tonnes of waste a day. Only 40% of that is formally collected. And enormous amounts of rubbish lay around almost everywhere.

REPORTER: There is so much rubbish here, what does that tell you?

DR TAOFEEK FOLAMI:  Yes we will talk about that. That's the essence of the santitation issues. These are the practices that we want to dissuade people from doing, essentially throwing bottles and litter into the gutters. That is what is blocking the drains.

But rubbish is just one of many concerns for residents here.

MAN:  The street is no good, we are suffering for water here. State government, we need this street - we are suffering for this place. We are suffering for these streets.

DR TAOFEEK FOLAMI:  Even the inhabitants of the area they find it difficult to move. They feel that they are being neglected.

Dr Folami says rapid urbanisation has forced his government to play catch-up.

DR TAOFEEK FOLAMI:  In Lagos state we have about 9,000 roads in our road network and we are constantly building. This is one of them. 20 years ago there was hardly anyone living around this area.

As we head to the bus, I'm surprised about how up-front the government is about its challenges.

DR TAOFEEK FOLAMI:  You can imagine Australia's population is 21, 23 million and they got to that population in about maybe 100 years or whatever. We have to deal with our rapid rate of urbanisation in a very short period of time. Within one generation. We know the challenges, we know what to do, we're trying very hard to do so.

With its ambitious projects and a burgeoning population, Lagos may be poised to become Africa's model mega city, but the overriding challenge now is to ensure that no-one is left behind.

Reporter/Camera
Yaara Bou Melhem

Fixer
Anthony Abbey

Producer
Nick Olle

Editor
Micah McGown

Additional footage courtesy of Eko Atlantic, NLE