Most programs use a 4 month or 3 month season-  we recommend a combination of aerobic and anaerobic sets during each cycle. Early in each cycle, focus predominantly on aerobic sets (50%): around 1500 to 2500 yards with rest base of 25 to 30 percent (example: if an athlete swims a 200 in 120 seconds with 2 minutes, his rest is 30 to 35 seconds. 

Midway through the cycle, we recommend a combination of sets - splitting the two into 25% per set, distances around 1200 to 2000 yards with rest base of 15 to 25 percent.

During the last part of the cycle, most (if not all) sets should be anaerobic, ranging 800 to 1200 yards. We recommend focusing on sprints and game-like situations with a higher percentage of rest (such as 35 to 40 percent). 

It is also important to incorporate water polo elements into the swim sets. Examples: Rico Turns, progressive speed, change of speeds,etc.

According to studies done during the 2016 Olympics (tracked by cameras and GPS, the average player that swam most of the game swam just under 1000 meters, with only 45% of the game in the horizontal position.  Don't be afraid to focus on quality vs quantity in your swim training.