Need some fish location advice..  When looking at a good quality lake map or at a graph with a good mapping chip, are there any contour shapes/patterns/signatures that can reliably indicate hard bottom?  I fish a lot of milfoil-matted natural lakes in the upper midwest.  Identifying hard bottom along the weed edge is straightforward enough - brighter coloring on a well-tuned side image.  But what about firmer areas that are buried up underneath the foil?  SI can't penetrate to see them so I'm wondering if they might be identifiable, once the boundaries of a good foil mat are known, using map contours (irregularities, presumably) under the mat.  If contours aren't the answer, what are the best ways to find buried-up hard bottom spots inside of big milfoil beds?  Thanks for your insights, all..

Rick
Plymouth, MN

Welcome to the Forums Rick! I'm not sure if you can verify bottom hardness just by structure alone. However you can run through an area early in the spring before it gets too thick or late in the fall after the foil has died off. Mark the hard spots with side imaging, and then you know exactly where they are. The hard spots aren't going to change position from year to year like the grass can/will, so once you have them you can see where they line up with how the grass is growing at the time. 

Start by looking for steeper contours - where the contour lines are closer together.  Soft bottom doesn't usually form steep drop-offs as often as would a hard bottom.  Of course this will just be a better probability.

8 hours ago, MinnRick said:

SI can't penetrate to see them so I'm wondering if they might be identifiable, once the boundaries of a good foil mat are known, using map contours (irregularities, presumably) under the mat.  If contours aren't the answer, what are the best ways to find buried-up hard bottom spots inside of big milfoil beds?

Traditional sonar will show you this.

If you are in vegetation mats, your transducer is below the mat so 2D sonar will show hard/soft bottom areas.

If you are above thick submerged vegetation, the sonar pulses will be blocked by the vegetation.

 

Thanks for the feedback!  Think I'll give traditional sonar a try.  I recall reading somewhere that harder bottom spots can sometimes thin out the foil growing out of them a bit, which just might make those areas (or some of them, anyway) easier to ping through.  Seems reasonable enough and you'd just need to catch a quick glimpse of a double-echo to potentially have a sweet spot.  Experiment, experiment, experiment..

Tight lines all.