Depth and position information was recorded using the GPS / Fishfinder logger fitted to my boat. Using VBA in Excel, this was converted into KML and could be viewed in Google Earth.
The colour of each datapoint is related to the depth recorded (green is shallower, red is deeper); the radius of each datapoints is also proportional to the depth recorded - the depth reported by the fishfinder being the shallowest return within the cone of the transducer characteristic.
This plot is of the mouth of the River Arun:
A is a shallower area of the river where longshore drift has pushed shingle over the river wall from West Beach (B) and formed a shoal.
C is a bit of an anomaly and I can only think that there was something floating underwater.
D is the main channel of the river.