I have a Garmin Etrex that with the right maps loaded can show lake depth, terrain elevation, speed, altitude, etc. The screen is pretty small & interesting to read sometimes.
And I have a Garmin Streetpilot that shows all the streets, speed, Bluetooth handsfree, & MP3 playback. The screen is twice the size & very easy to operate. But there are no maps available for it to show details in the lake.