Volunteers keeping the River Wensum tidy collected 16 black sacks of litter on their latest clean-up - and a submerged motor scooter.
Norwich RiverCare, which was set up in April, carried out a routine litter pick around the river on Saturday and collected 16 bags of rubbish.
They also unearthed a motor scooter, which was sat on the river bed, an inflatable - though now deflated - alligator and drink containers.
Though the group take part in regular litter picks, it came as part of the Great River Rescue, a national campaign running during October encouraging people to look after their rivers.
Lottie Williams, programme officer for the national RiverCare and BeachCare programmes, said: 'It's not unusual for groups to pick up this much.
'You do find that once you've cleared it up, a month later there's a lot back there, and we're aware that local people are also clearing what they can in them meantime.'
She said people sometimes assumed others would pick up litter after them, and were not aware of how long it could take for items to biodegrade.
'Cigarette butts can take about 12 years to biodegrade,' she said, 'and that's incredibly damaging. It's a concern that the more polluted our waterways get, it becomes more unhealthy for our wildlife.
'The river actually becomes a wildlife corridor into urban areas, so particularly in the Wensum it's so important if we want to keep wildlife in those areas.
'They can be strangled, choke and ingest what we throw away.'
The RiverCare group, which has grown each month, also marked the start of National Mammal Week by installing a mammal raft along the water near the Marlpit Pub.
The small floating platform is anchored to the bank and uses a tray of clay to record the tracks of animals visiting the raft - and they hope it will confirm the presence of otters in the area.
The Norwich group is part of the national RiverCare and BeachCare programmes, run in partnership with Keep Britain Tidy and Anglian Water.
The numbers of the group have been growing at each event, with the team setting up a variety of events in the last six months.
• If you would like information or to join the group, contact its organiser Stuart Stebbens on stuart-norwichrivercare@outlook.com
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