London School of Diving, based in Chiswick, has set up the specially adapted bike on the bottom of its training pool for the challenge, which started on 1 February and runs until 21 March.
In the LSD Mile event, individuals or groups are asked to complete a mile on the training bike while dressed in scuba gear.
A slot can be booked at the centre once at least £100 in sponsorship has been raised.
Non-divers can take part but will need first to complete a try-dive and assessment with LSD.
All rides will preceded by a safety briefing and watched over by a safety diver.
The winner of the LSD Mile will receive a £200 voucher from London School of Diving which may be redeemed against any of their recreational courses.
Juniors, aged at least 12, can complete a Mini Mile event, having raised at least £50 in sponsorship.
To enquire about participation, call LSD on 020 8995 0002 or email to info@londonschoolofdiving.co.uk
Those willing to give sponsorship as non-participants can do so via LSD’s Sport Relief web page at www.mysportrelief.com/teamlsd