Why does water aerobics burn so few calories?

keobooks

I work out 4 days a week doing water aerobics. 2 days in shallow water and 2 days in deep water. I feel like I am really burning up calories! And I even work up a drenching sweat on my forehead ... The rest of my body iis too cold from the water to do so. I feel worn out in a good way after each workout.

But when I log it, it says I only burned 400 something calories? That's only a little bit more than walking! I feel slightly disheartened that I work so hard and burn so few calories.