Yes — a regular DSLR like the Canon T2i can be used underwater, but it requires a waterproof housing. For a true DSLR setup, you typically need:

• a camera housing made for the T2i
• a matching lens port for the specific lens you plan to use

That’s the core requirement. The main tradeoffs are cost, depth rating, and how many camera controls remain accessible underwater. Higher-end housings are expensive but allow deeper use and more control; simpler soft-case style options may work for shallow snorkeling but usually have lower depth limits and fewer controls.

If you only plan to snorkel, a simpler waterproof case may be enough. If you want to scuba dive or go deeper, you’ll want a proper hard housing rated for that depth.

Also keep in mind that underwater photography has a strong color-balance challenge: water absorbs warm colors first, so images often look very blue unless you correct white balance or add lighting.

Because housings for DSLRs can cost a lot, some people choose a waterproof compact camera instead, especially for casual underwater shooting.