A traditional sonar unit with dual frequency will have coverage that is equal to the depth or 1/3 the depth depending on the frequency.
A unit with the side looking imaging technology will have more coverage since it is Range adjustable. Cost more though.
Sonar will not see through heavy grass, it will look like the bottom is fuzzy.
Same location on a weedline with Side Imaging, Down Imaging and traditional 2D sonar:
Humminbird Helix 12 SI, 1198c SI, 1198c SI, ONIX 10 SI NT, 360, RC-1