Sand tunnels and arches?

[npgeorge]

So, did my first OW dives this weekend without a DM present. Was a ton of fun but definately a challenge with task-loading like navigation dealing with the float, etc. Loved it none-the-less! Anyways, we went to a few lakes in Northern Wisconsin including Crystal Lake and Paya Lake near Crivitz. The water was fabulously warm (above 30ft) and with extremely good visibility. While what we saw was standard fare for a wisconsin lake, panfish, smallmouth, greenery, etc. At Paya lake we saw something very interesting. Unfortunately, we don't have pictures so I will have to explain it from memory: So here's the scoop. At Paya, the depth we spent most of our time at was between 20-30ft riding the 58deg thermocline. After about 20ft Paya transitioned to a muck bottom. Going north/north-west towards deeper water we found a depression in the muck that appeared to be compacted sand running towards shallow water (prolly 50ft long?) Anyways, the sand was riddled with archways and passages/tunnels of ~1-3 inches in diameter. No cold water or anything was found eminating from the tunnels, although strangely the sand was very compacted, almost like a sandy clay. My question for any of you freshwater divers, or those in-the-know, what do you think made these tunnels. Most of the tunnels appeared to interconnect and were anywhere between 6inches to a few feet between entrances. My first guess is some form of transient cold springs or something. What do you think?

 

[BNow0707]

When diving freshwater rivers and such around here i have noticed holes in the muddy bottoms. They are usually smaller than what your referring to about a 1/2 inch to and inch wide. But they are usually 6in or less apart. It was always my guess that it was "escape holes" for gases from decomposing materials. If you have ever waded in shallow waters in some spots where there are large deposits of plant materials underwater simply stepping near the area will release large ammounts of trapped gases.

This may or not be the case but just my 2 cents.

 

[npgeorge]

might've been gas escape or something, but it was extremely odd that the tunnels ran laterally and only through the sandy stretch of the lake bottom running back towards shore. Kinda makes me wonder if something (current, spring, animal) cleared off or excavated the muck bottom away leaving sand. The weirdest things were the holes that were so close they formed miniature arches. Kinda screamed that it was something biologic. (Funny thing is I'm a microbiologist/biologist and I'm completely stumped.)