This thread got me thinking... which means two things. I am going to break something for sure and its going to cost me money.
I rented a 4" trash pump this past weekend and tried a couple of things. The best "experiment" was my under water beach cleaning. (I took some before pics and forgot to take the after

. I will take it later this week and post them both)
The beach is a small area (approximaterly 900 sq ft under water). We placed the pump inlet hose 6" under the water in 1-2' of water. Then simpley walked and raked to suspend silt and other organic materials. We did this for about 1.5-2hrs. Very pleased with the results.