What exploded over Lake Huron?

On July 31, 2008, something exploded over Lake Huron. The explosions triggered several audio monitoring devices as far away as London, Ontario. From the London Free Press:

Highly sensitive devices installed near Lucan by Western to monitor low frequency sound waves detected a series of four impulses that lasted about a minute, starting at 11:12 p.m. on July 31.

Five minutes later a low frequency rumbling was detected coming from the Kincardine area.

Trouble is, nobody knows what caused the explosions. While numerous explanations have been proposed - sonic booms, meteors, the local nuclear plant- all have been discounted. So what the heck was it?

One alert MetaFilter contrib, short of providing a solution, points out a strange parallel. In late July of this year, an Inuit Ranger camped out on Baffin Island reported hearing a large explosion, and witnessing a residual plume of black smoke. The blast also reportedly killed several whales.  The Canadian Military was sufficiently concerned to dispatch a helicopter to the scene. Unfortunately, they were a week late and could not find any traces of the blast.

So what's the explanation? Secret weapons tests? Alien invaders? I'm going to propose something a little less exotic. Both events may be examples of a resurgence in blast fishing. This highly illegal technique involves dropping dynamite or some other explosion into water near schools of fish. The pressure waves kills the hapless creatures, and they float to the surface for easy collection. So is someone blast fishing on Lake Huron? And more troubling, is somebody illegally poaching whales in Canada's Arctic using explosives? Clearly, somebody needs to look into these events a little more closely.

Until then, I guess we'll have to keep our ears and eyes open for more mystery blasts.