There are two pools open to the public in Lagos.
1) The new olympic size pool between the old Pingo Doce and Mcdonalds/Seagulls Swimming Pool roundabout.
2) The pool at the Bombeiros (Fire Station.)
I swam in the former a year or so ago.
I have not checked either out over the past year or so.
Am v. busy at present but will try to find out more in the next week or so.