I like this swim because it typifies what you will encounter on race days with surges and recoveries. Many triathletes do not know how to recover while swimming (swimming easier) and this set teaches that, especially since the rest interval is so short.
Warm-up
200 swim easy 200 kick 4×50 as 25 easy/25 fast
Main Set
8×125 with 5 sec rest as (50 moderate, 25 fast, 50 easy) 100 easy 4×250 with 5 sec rest as (100 moderate, 50 fast, 100 easy) 100 easy
Cool-down
200 choice
Total = 3,000 meters