If you're a regular visitor to one of the Illawarra's northern beaches, chances are you've spotted Conrad.

He's the grey-haired man with the scruffy beard who wanders, bare foot, picking up the bits and pieces beachgoers leave behind.

Conrad has a theory about people and littering.

He insists it's no mistake humans throw away a scrunched up sandwich wrapper or an empty drink can.

It's the way we're built.

"It's humans fulfilling a subconscious need to leave a mark," the 68-year-old surfer explains when interrupted during one of his impromptu patrols of Bulli Beach.

"I see it time and time again. Even when they make a big effort to clean up after their big gathering or a picnic. Everyone pitches in and cleans the area but they will always, always, leave one thing behind.

"It's amazing, I see it over and over. It's almost bizarre. And if a place is already a mess, they leave a bigger mess."

Conrad - real name Graham Smith - has been watching the behaviour of humans since he was a young grommet on the hunt for the perfect wave.

Nowadays northern suburbs residents, exercise groups and the mums in the playgrounds are used to Conrad being not far from a rubbish bin.

"I'm sure I was only a teenager when I first started thinking about it. I'd see a piece of glass and think: 'Gee someone is going to cut their foot on that broken glass', so I just started to pick things up myself," he recalls.

"That's when I remember thinking this has really got to be stopped. Parents should be able to come to the beach and not expect their children will get hurt.

"I'm not the only one and I never have been - I remember other people cleaning up. I'm nothing special."

But you would be hard-pressed to find someone who devotes so much time to the task of picking up after complete strangers. Every day Conrad hits the beaches and the cycleways.

"It gives me a feeling of freedom," he explains.

"I just get down to the beach and I pick it up, pretty well. I can't help it. It's become a compulsion. I hate to see the mess. If it's clean I'm happy."

Conrad is constantly amazed by the actions of people who don't think twice about using their precious landscape as a dumping ground.

"I guess you can understand the behaviour of people who've had takeaway and can't be bothered going to a bin; they're leaving their mark everywhere.

"But every now and then you see something bizarre. One day I found a huge cupboard door mirror, a broken mirror down on the beach."

While Conrad is on an endless quest to rid the land of litter, he only wishes he could provide the same care for the oceans and waterways.

"Let's give the fish and the birds a chance," he says.

"All this rubbish in the ocean, most of it comes off the land, it gets washed in.

"The amount that was there from the last flood, it's incredible. You spend a week cleaning up and you think: 'Why is it here?'

"At some stage people are making money, these fast food chains, you've got to think if they want to make money they should be paying for the clean-up."

CSIRO researchers have surveyed more than 35,000 square kilometres of Australian coastline and found no beach on the continent was free from rubbish.

CSIRO researcher Chris Wilcox said plastic dominated the rubbish.

"The whole coastline is connected by the ocean, so something we do in Sydney and Melbourne ends up affecting thousands of kilometres of ocean and thousands of kilometres of coastline," he said.

The recently released CSIRO study found concentrations of rubbish on the coastline and in the water increased around populated areas.

"Eighty per cent of the debris comes from urban sources and 40 per cent of that is beverage containers," Dr Wilcox said.

"The beach is often where debris starts its journey and can end up in large concentrations in the ocean," he said.

"Big eddies called gyres [large systems of rotating ocean currents] trap debris and can lead to large concentrations of floating rubbish.

"One of the gyres which has been extensively studied in the Atlantic has densities of up to 588,000 items per square kilometre. We surveyed off the coast of Australia and found densities about a tenth of that, about 50,000 things per square kilometre."

The study found pieces of debris have a pervasive impact on marine life.

"We found 80 seabird species that have been detected eating plastic and 60 per cent of these birds had plastic in their gut at the time," he said.

Dr Wilcox said the majority of debris was from land-based activities.

That means with a "Conrad" stationed at every Illawarra beach we could make a real difference.

For now, the Bulli identity will carry on his work, without asking for any praise or pats on the back.

All he'd ask is that each one of us stops and thinks before leaving that plastic straw, empty drink can or plastic bottle where we last had use for it.

"I want to believe it's getting better, that people are thinking twice and putting their rubbish in the bin. And considering how many more people are around these days, then I think maybe it is."

He doesn't feel resentment towards the litterbugs that keep him busy.

"If I get angry I'll get away from it and do something else," he said.

"I came to realise that if I pick up rubbish when I'm in a bad mood I get a sore back.

"A lot of people say: 'You do a good job'. I don't expect other people to do it, but it does tend to make people put their rubbish in their bin when they see me out and about, so I won't lie, that's a bonus."