The National Landlords Association (NLA) has revealed the results of a fundraising project.
Some £500 was raised for Thames21 - a waterways charity in the capital.
Money was donated from NLA employees rather than them sending Christmas cards to each other and to clients last year.
Chairman of the organisation David Salusbury said: "With our offices overlooking the River Thames, the NLA team has risen to the challenge of raising money for this well-deserving charity which makes such a difference to communities across London."
According to the chief executive of the charity Debbie Leach, some 8,000 volunteers have taken part in clean-up activities for Thames21.
More people and businesses will hopefully be encouraged to protect London's waterways, Ms Leach added.
Thames21 volunteers carry out work such as graffiti removal, cleaning up "grot-spots" and community education.
Long-term change is hoped to result from their work and regular river clean ups are open to all, the organisation adds.
Written by John Weeks
