1 cup twice a day sounds about right but I would use fillers (green beans, pumpkin) to replace the other cup. He is a big dog and still needs quite a substantial amount of food to sustain.
I would also cut out all treats. If you need to treat him, use bits of his kibble.
Swimming is excellent exercise and I would definitely keep that up. Aim for an hour of something vigorous every day. Running with you or another dog is excellent, retrieving, swimming, long off leash walks, etc.
Awww Bruce...it won't take much to take the weight off.
Lucy is very active everyday and I only give her just under a cup 2 times a day. She does get treats daily and extras like fish and cottage cheese but only on really super active days.
The green beans work great for filler.
Good luck with getting the weight off.