Absolutely ...
Sonar reflects off anything that is of a different density than the water itself ...
The more the difference in density = the more the sonar will reflect ...
So some substances may reflect more sonar (wood, gravel, metal, concrete, etc) ...and show bright hard return echoes ...
Softer substances will also reflect sonar but to a lesser degree (mud, algae, plastic, water logged wood) ...and show Softer return echoes ...
Rickie