Eat right and swim right
Here are some more ideas … try doing an audit of what you consume during the day. Enough water/ Plenty of fruit and veg? The right amount of protein?
2 hours, 4350m, Front Crawl, Enduration
Quite a distance in a couple of hours.
90 mins, 3000m,
Front, Back, Breast – 50m swims, building pace, reducing rest