Buying raw land with wetlands?

[Tyler D.]

I recently came across an opportunity in my town. There are two large pieces of land for sale for relatively cheap. 

The first is 5 acres, and mostly wetlands. The 2nd is 1.3 acres, with some wetlands. I did a walkthrough and both appear to have a decent amount of usable space. Both are for sale at $40k each. This is in a town where SFH-ready lots go for 50-100k for much less space.

Given then each lot is very cheap, and is in a decent area, I'm considering buying one or both pieces of land. My primary use would be to hold it as is, and possibly develop in the future. My area is appreciating quite quickly and there has been more and more construction over the years.

If I were to go for it, what should I do for due dilligence beforehand, and are there any major red flags I should be aware of?