On you favorite reservoir lays under the water several man made objects. One of the best fish holding structures on lakes are old road beds. These roads can be asphalt or clay and rock but most all of them have several factors in common.
 

Road beds have drainage ditches along both sides to channel the water off the roadway when it was a road before the lake was built. These drainage ditches will drain along side the road to a culvert or creek channel which will pass under the old road. This is what  I call the sweet spot, culverts and bridges give the fish a place to hide and ambush their pray.
 

To find the culvert or bridges mark the road with 3 to 6 WayPoint Markers for a distance of several hundred yards then simply graph along side the road looking for where the depth achieves it deepest depth and then comes back up. Then turn around and cross the road at a 90 degree angle and you should see a dramatic change in depth at this point indicating either a culvert or bridge is present. Place a WayPoint Markers on the top of the Road Bed. This is the sweet spot (critical area) and again you have found the fish.

PRADCO bass fishing pro Jimmy Mason of Rogersville, Alabama explains the importance and functionality of marker buoys. Jimmy lists them as one of the most important pieces of equipment he couldn't be on the water without having them in his boat!