If you are looking for a nice day trip from 2 - 4 hours or more try this. You launch your kayak or canoe at a nice sandy spot on the Connetquot River. It is a small, brackish, tidal river that empties into the Great South Bay on the south shore of Long Island. Conditions can vary greatly depending on wind and tides.
Once in the water, if you head west, you can follow the river a short distance and enter into the Grand Canal which is a vestige of the Vanderbilt estate in Oakdale. This is a quite short trip but you can make it last by exploring. If you head east, you can go into the bay and skirt the shore where there are many small canals leading inland. Some of these small canals end in desolate, beautiful locations where you seem to be the only one on the face of the earth, when in reality you are surrounded by busy towns and people.
The area is extremely busy with power boat traffic during the warmer weather, especially on the weekends.
Various motels etc. in the surrounding towns.
On Long Island - Sunrise Hwy (rte 27), east or west to Heckshire Parkway south. Exit at Montauk Hwy (Rte 27A) heading east. Turn right at the first light, on to Great River Road. Continue on G.R. Road and make a left just before you enter the golf club called Timber Point. The dirt road leads a short way to the waters edge where there is ample parking.
Mapquest gives a good over view of the area and the canals but it is not always accurate.