The Kenya Coast Guard Service (KCGS) has raised the alarm over increased dumping of plastic waste in the Indian Ocean and on beaches.
A similar situation has also been reported in rivers and lakes on the mainland.
KCGS Director-General Loonena Naisho said perpetrators of marine pollution will be dealt with.
He mentioned beaches in Lamu, Malindi, Kilifi, Kwale and other coastal areas as choking from mostly plastic waste.
Poor plastic waste disposal has also been seen on Lake Victoria in Kisumu County, Naivasha, Thika, Mara River in Narok and other areas, he said.
He stressed the need to desist from dumping plastic waste in water bodies because that directly endangers the marine ecosystem.
The coast guard, he said, is working with other agencies on an initiative seeking to promote awareness on plastic waste through various activities.
"I'm unhappy with the rate at which our beaches and the Indian Ocean is being littered with plastic waste. Plastic materials are dangerous," he said.
"They cause a serious problem to our marine environment and health as a whole. We need to desist from careless dumping of plastic waste in our water bodies, be it the Indian Ocean, rivers, lakes and springs."
The initiative will involve the public, including schoolchildren, in frequent beach cleanup campaigns, he said, adding that the law will be enforced and people found dumping plastic waste will be prosecuted.
Mr Naisho lauded the August 2017 ban on plastic bags, saying it has helped in ensuring a cleaner environment.
But he proposed that legislation be enacted to totally ban single-use plastics.
His sentiments come as environmentalists in Lamu, led by Taka Taka Foundation, have introduced a competition called Okota Plastiki (collect plastics) in which residents are encouraged to collect plastic waste in exchange for cash.
The campaign is generally meant to fight the growing problem of plastic waste being dumped carelessly in the Indian Ocean and on Lamu beaches.
The environmentalists have also been agitating for a total ban on single-use plastics, saying many towns, beaches, national parks, forests and conservation areas are filled with plastic waste, mostly plastic water bottles, disposable plates and cups, cutlery and straws.
"Poor plastic waste disposal is still a challenge in Lamu, the Coast, Kenya and the world as a whole. We are doing what we can at the community level," said Taka Taka Foundation spokesperson Ali Skanda.
"But I think it's high time the Kenyan government introduces a total ban on the use of single-use plastics to reduce the amount of plastic waste still finding its way into water bodies. That will be the only way to achieve a plastic-free environment."
Hoteliers in Lamu Old Town are also concerned about the plastic waste build-up on beaches, a major tourist attraction.
Former Lamu Tourism Association chair Ghalib Alwy said a filthy environment discourages visitors.
"The county government should formulate better plastic waste disposal policies. Regulations should also be introduced to deal ruthlessly with any form of environmental degradation in our county and country," he said.
The areas of Lamu most affected by plastic waste dumping include Lamu OId Town, Matondoni, Kipungani, Mokowe, Wiyoni, Kiunga, Ndau, Kiwayu, Kizingitini, Faza, Pate and Mtangawanda.