Ok, so this deep water cattail situation still wasn't registering to me. So I found a couple references that suggest one species grows in deeper water than the other:
Typha angustifolia(narrowleaf) generally occurs in deeper water than Typha latifolia(broadleaf). Typha angustifolia(narrowleaf) has fewer and larger rhizomes, resulting in a low rate of cloning but enabling it to grow in deeper water than Typha latifolia. Typha angustifolia has a higher allocati onto sexual reproduction. Cattails spread both vegetatively and by seed, particularly underdrawdown conditions
Where Common Cattail and Narrow Leaf Cattail are found together, they are frequently segregated by water depth, with Common Cattail found in shallow water and Narrow Leaf Cattail in deep water, usually more than 2½' deep.
I'm assuming I have the common broadleaf cattail, which doesn't spread as fast, nor does it grow in as deep of water.
