LISA DESAI: It's just after sunrise in the coastal town of Zarzis in Southern Tunisia. Tourism and fishing are the staple of the local economy. And the fishermen sell their catches of dorado and tuna, in the early hours of the morning.

Here on the Mediterranean Sea a problem plagues Europe and many African countries. And it's been growing since the civil war began four years ago in neighboring Libya.

A mass exodus of migrants and refugees from the Middle East and Africa have been drawn to Libya, where a lack of central government authority allows human smugglers to operate freely.

The migrants make the dangerous journey on the Mediterranean with one goal in mind: Landing on European shores.

Wooden boats and inflatable plastic rafts, often overflowing with migrants, have been sinking one after another, claiming thousands of lives.

And these men have found themselves on the front lines of a humanitarian crisis.

"We're on a Tunisian fishing boat in the Mediterranean Sea. The fishermen here say that over the last six months alone they have rescued more than 500 migrants on the verge of drowning."

SLAHEDDIN: One time we rescued 10 migrants. When they got on the boat two of them started praying. It gave me chills, all over my body.We are fisherman. We are here to make a living. We are not here to rescue people, but we have a feeling of humanity. So if I find someone on the sea I will save him.

LISA DESAI: But even without the right equipment, the fishermen say they can't turn away from migrants lost at sea. They stop their work to bring them to safety on the Tunisian shores and pay for extra fuel to get them there.

Sometimes these untrained fisherman risk their own lives pulling people out of the water and spend all night waiting for help from the Tunisian Coast Guard.

SLAHEDDIN: It's a powerful feeling to see someone helpless, hungry and being burned by the sun. It's very hard, you are in front of someone who is calling for help.

LISA DESAI: Mongi Slim, is the head of the Zarzis office of the Tunisian Red Crescent – the Red Cross in Muslim countries.

At the local fishing association he coordinates rescues in Zarzis and other nearby port cities like Ben Gardane.

MONGI SLIM: Those people are fighting, each one wants to go first.

LISA DESAI: And I see some pictures here of the bodies washed up.

MONGI SLIM: Yes, this, this here is in Ben Gardane. These are Syrian people. Here is in Il Kitif, the port of Ben Gardane. We received this day 54 bodies from Syria.

LISA DESAI: Photo after photo shows overcrowded boats men and women fighting to stay alive, and migrants desperately flagging ships for help.

When the fishermen find the sinking boats, if they are close enough to European waters, they call the Italian authorities, but sometimes, the Italians don't show up.

MONGI SLIM: He had to rescue them himself, because nobody come. And he waits a long time and nobody come, and people are crying in the sea, and he must help them.

LISA DESAI: The lucky ones who make it to Zarzis alive get help from the Red Crescent.

Mongi earns his living as a pharmacist, and has made it his volunteer mission to provide the migrants with shelter, food, and support to survive.

Can you tell me how many people live here?

MONGI SLIM: In this house, we have four.

LISA DESAI: 18-year-old Tuba – on the right — is from Senegal. How did you end up here in Tunisia?

TUBA: We were trying to go Italy. We left Zwara to go to Lampedusa.

LISA DESAI: Do you remember the day that you were rescued? What happened?

TUBA: We saw lots of boats. We were trying to call them, but they didn't respond.

LISA DESAI: There are now several hundred migrants and refugees from Africa and the Middle East living in the area around Zarzis.

Many fled war, poverty, or persecution in their home countries.

Some stay only a few weeks, before walking 80 miles across the border to Libya to board boats bound for Europe one more time.

Ousman Kebbeh is from Gambia. He journeyed by sea to Europe three times. The first two times, he didn't get far…he was rescued and returned to Libya. During his final attempt, he was saved by Tunisian fishermen.

OUSMAN KEBBEH: We just waiting for our deaths, no options. You just inside the boat waiting for our time to die.

LISA DESAI: The fishermen sent us this cell phone footage that shows Ousman's rescue. He was on board a plastic raft, crammed with 90 other people heading to Italy. Eventually, the boat sprung a leak and slowly began to fill with water.

OUSMAN: The water is entering inside, and the waves is coming again, the water is coming up. So the water is coming different directions. You don't know where exactly water is entering the boat. So it's a terrible situation.

Some people are vomiting, some people are crying, some people are fighting because you become crazy on the sea. You become different man. So I was just thinking two things, that I will survive, or I will die. This is it.

LISA DESAI: Like most migrants, Ousman had put his fate in the hands of human smugglers, who typically leave the migrants to drive the boats themselves.

The journey can take more than 24 hours, They have few tools to navigate, sometimes relying on just a compass to find their way to Europe.

In Zarzis it was common knowledge that one of the ways that smugglers lure migrants is by advertising on social media with posts like these , featuring pictures of cruise ships– they promise a safe journey, with children riding free.

This post, which was recently taken down, lists the price per adult: a thousand dollars to be ferried from Libya to Italy.

Ousman is one of thousands of migrants who have flocked to the war-torn country based on the promise of making it to Europe. But once they arrive in Libya, they are caught in violence and lawlessness and have no choice but to risk their lives on the Mediterranean.

OUSMAN: You cannot live in Libya. People in Libya they just keep on harassing Black people, keep on beating them, keep on lock them.

Some of them kidnap you in your houses, lock you. You have to pay money for them otherwise they'll kill. So the only thing you have to go, you have to cross to Italy. This is a problem. Libyan situation is worse, because there is no government, nobody is control.

LISA DESAI: Last year, the Tunisian Red Crescent took in 700 migrants, and so far this year the number has already doubled.

Mongi Slim is worried about how to handle the growing number of migrants ending up in the port city of Zarzis.

MONGI SLIM: Nobody now is helping enough this people. Our government also, we don't have any shelter here to this people. When they arrive, we have a big problem to resolve the shelter.

MAN: The dream is to make a better life than they have in there country, and they want to support their family, but I think that they cannot get it.

LISA DESAI: The fisherman say they will continue rescuing migrants.

SLAHEDDIN: It is risky for us, because there's bacteria, disease and people are afraid. But it is a humanitarian duty, and we do it willingly.

LISA DESAI: The fisherman on this boat helped save Ousman from drowning.

OUSMAN: They are good people, they love the sea, so they can't just see people die and leave them like that. They save many lives in the sea. Not only us, but many people. And I hope they are still doing it.