The spring clean, which is an annual 10-day campaign, involves over 2.1 million people nationwide in thousands of events. The group says this year will be the biggest ever.
The launch project for the campaign - The ThamesClean partnership between Tidy Britain Group and the new Environment Agency - is entering its third year.
Professor Graham Ashworth, director general of the group said: 'Although the water quality of the Thames is better than it has been for hundreds of years, the Port of London Authority still collects over 3,000 tonnes of litter from the river each year which costs over half a million of pounds.
'National Spring Clean provides an ideal opportunity to raise awareness of the problems caused by litter,' he added.