Laden with medicines, the speedboat sets off before dawn, its path lit only by the full moon as it cuts between miles of thick mangroves towards Kenya's border with Somalia, where few dare to go.
Two hours later at sunrise, the boat arrives at Kiangwe village, one of several remote coastal communities whose only healthcare comes from these monthly visits by the Safari Doctors mobile medical team.
Volunteer doctors and nurses roll up their trousers and heave containers full of medical supplies onto their shoulders before wading ashore and hiking up a hill to a building that will serve as their clinic for a few hours.
Kiangwe and surrounding villages have been hard-hit by the Kenyan government's war with Somali extremist group Al-Shabaab, whose militants operate from within the nearby Boni Forest which straddles the border.
In the distance, between stick-and-mud houses topped with palm fronds, stands a shuttered clinic that was built but never occupied.
"We have several buildings laying dormant because we have personnel (professional nurses and doctors) that don't want to get posted" to the region, said Umra Omar, the 36-year-old who founded Safari Doctors four years ago.
So, every month, over a few days, her voluntary team made up of both Kenyan and foreign medics visits up to 12 villages, some of which require a last-minute phonecall to check on security.
However four other villages in the region are considered no-go zones and have no healthcare access at all, said Omar.
Thanks to donations and fundraising, the Safari Doctors mobile medical team treats up to 800 patients a month.
Inside the makeshift clinic, the team sets up a triage area where patients are weighed and have their blood pressure taken, before being directed to one of several desks manned by medical personnel.
At one desk, a group of nurses crowd around a woman with a hard lump in her neck, believed to be a bullet lodged there from an Al-Shabaab ambush on a car she was travelling in several years ago.
"I was the only one left... others had died on the spot," Bilai Abdi said of the attack, which also left her with bullet wounds in her foot.
The nurses advise her to go to Lamu to get the bullet removed. Asked how she will do so, she just shakes her head.
Rufia Alio, 55, sliced his finger open while farming over a week before the mobile clinic visited, and is finally getting it bandaged up.
"There are no hospitals here which is a problem. We have pregnant women here, we have the aged ones who are suffering, there are others who suffer from fever... and thus when Safari Doctors come they help by giving us medicine and injections," he said.
However once the Safari Doctors move on, there are few options.
Omar tells of a young man from Kiangwe who carried a sick villager with appendicitis on a 24-hour journey by motorbike in order to get him to a hospital.
That journey costs about $30 (27 euros), but the road is dangerous and prone to Al-Shabaab attacks, while communities on islands have no access to a road.
Hiring a speedboat to Lamu town can cost up to $200 - a fortune for members of this community who mostly live off the land.
Omar said that for a woman in emergency labour, the bumpy speedboat ride is "something else", while some have even given birth in the middle of the ocean.
In a bid to plug the gap, Safari Doctors has trained traditional birth attendants and given youth in the communities basic first aid training.
Lamu County has long been one of the poorest, most underdeveloped, and marginalised areas in Kenya.
Locals say their plight has only grown worse since the army in 2015 sent troops into the area to flush Al-Shabaab militants out of the forest, in what was meant to be a three-month operation, but has yet to come to an end.
The Al-Qaeda linked Al-Shabaab has staged several bloody attacks in Kenya, including in Lamu, in response to Nairobi sending troops into Somalia in 2011.
It is believed that a few hundred members of a Kenyan Al-Shabaab affiliate are living inside the forest.
"Ever since they (security forces) came, we can no longer go and earn a living from the forest like we used to before which was our way of life, harvesting honey," and hunting, said Alio.
The clinic is not only the sole option for villagers, but also for the soldiers fighting Al-Shabaab, whose operation has been plagued by poor co-operation, lack of equipment and demoralisation, observers say.
AFP saw a dozen soldiers at the clinic, some in uniform, some in shorts and flip-flops holding their rifles between their knees as they consulted the nurses.