How are regatta opponents selected?
Every race in each league is made up of 15 co-ops with the same amount of members with their Participate in Regatta status on.
If you join a co-op or check your Participate in Regatta status on after a race starts, you won’t be able to complete tasks and help your co-op race. That is true for all leagues and co-ops so that it won’t bring unfair advantage to some co-ops. Don’t worry you can always join your co-op to get a task in the next regatta.