Half of all regular smokers believe it is acceptable to discard cigarette butts down the drain - despite expert warnings about the risk it poses to marine wildlife, a survey has suggested.
A study for environment charity Keep Britain Tidy found 52% of daily smokers polled said they did not see a problem with getting rid of their cigarette butts in this way.
Meanwhile, only 53% of those surveyed said they realised ends would finish up in the sea when dropped down the drain.
Nearly two in every five smokers (39%) polled said they had discarded a butt in this way during the last month, despite 77% of them saying they were concerned that toxins from their cigarettes can harm marine life.
The survey of 4,146 people - including 502 smokers - was carried out by YouGov to mark the launch of Keep Britain Tidy's Flicking Blue Murder campaign, raising awareness of the link between cigarettes and the marine environment.
It comes after the BBC's Blue Plant II series, presented by Sir David Attenborough, which raised the profile of the oceans' plight.
Keep Britain Tidy chief executive Allison Ogden-Newton said: "Following Sir David Attenborough's rallying cry to reduce plastic waste on Blue Planet II, we wanted to show how simple everyday behaviour can affect the environment.
"While flicking a cigarette down the drain may not seem harmful, we need to ensure smokers understand that this has a direct and often drastic impact on wildlife.
"We need to challenge this view [that discarding cigarettes in this way is acceptable] and get the message to smokers that this is still littering.
"It's encouraging to see that so many smokers were very concerned about the impact of their cigarette butts on marine life, and we hope that this research will further educate the public about the effects of smoking-related litter."
Keep Britain Tidy and Sea Life Manchester will be creating an installation on Wednesday with three giant cigarette butts to show the effects of discarding such litter.