RobA,

Before the construction of my first pond (1995, 0.25 acres), I approached the NYSDEC about permits. Their response was that unless the pond was to contain 1,000,000 gallons, they didn't seem interested in (1) offering any assistance in its construction and (2) requiring permits.
Before the construction of my second pond (2004, 0.12 acres) I again approached the DEC only this time the procedure was a bit different.
Due to issues concerning wetlands, I had to submit a letter with a brief description of the project. I received a reply about two weeks later stating no permits from the DEC were necessary HOWEVER, the reply did note that I should contact my town officials AND the ACoE to see if any permits were required from those agencies.