Inspections are mandatory (and expensive) on Lake Tahoe. They must be done any time your boat is put in a water way other than Tahoe. They place a band around the eye hole of the boat and trailer so they know if the boat has been off the trailer since the last inspection.
Inspections are optional but free on some of the smaller lakes in the area. Once inspected and educated on how to keep the boat clean of invasive species you are given a sticker so you dont get stopped again.
The inspectors on Tahoe blocked several boats last summer from entering the lake due to zebra mussels found in holding tanks/ bilge, etc. They have decontamination stations set-up so even the boaters found with invasive species can get the problem fixed and go on with boating for the day.
Every report I have seen has been boaters or boats from out of state.
Apparently crayfish are also an invasive species in Lake Tahoe, a scientist just got approval to commercially trap them and sell as food to local eateries. Looking forward to some fresh caught Lake Tahoe crayfish tacos this summer!