Typical household pupose hydropower should not have to include massive restructuring nor re-engineering natural water systems. What it boils down to is sticking a small water-feed turbine into the moving water. People have been known to juice a water impeller out of an old washing machine and successfully use that as a motive device. This application would have a negligable to extremely low impact.
If required, one could dig out a side channel from the main flow, dedicated to moving your turbine. I'm not sure of the rules on this, but small is beautiful.

As to bears coming around eating up your house? Shoot first, and ask about it later.
I don't care what the rules are... there exists a more basic law of survival and of protecting your loved ones and possessions from harm, that supercedes any kind of local governmental paperwork protocols.

In support of Cliff's advice to tread carefully when building dams

www.snopes.com/humor/letters/dammed.asp

Propellors look deceptively easy to build, but are really really hard to make. NACA (forerunner of NASA) spent countless engineering hours of the first 50 years of the 20th century developing airfoils, pitch,chord, length-width ratio geometry, and so on, in order to get effective propellors on American airplanes.
The propellor is one of the most expensive single replacement parts in any windpower system, and with a reason.

Making a practical propellor is more than simply popping open a can of spinach, gulping it, and then spending 2 minutes of frantic fast forward time whittling on a log with a swiss knife in order to come up with something that'll fly.

Got a month?.......
, plenty of quality hardwood, and the patience of Job? Try very tediously utilizing templates, calipers, & plenty measuring just to get ONE blade right. Then comes getting the opposite blade to rhyme with precision to the first. Consider all the measuring, shaving a bit here, re-measuring, finding you've removed too much, then having to revise the first part, then ... well you get the picture. Making a mold of a perfectly formed blade in order to produce it's twin is possible... using fiberglass technology. And even then you'll need to apply small wights to get balance. Only this would still require more time/energy/dedication/skill than is possessed by the average DIY Joe.
......Anyway, lot's of specialized equipment required, as found in an aerospace plant.
>>Not a DIY project.

Just as you'd routinely balance your tires when mounting a new set, a propellor needs to have it's blades balanced with each other to within a few grams of criticality. I've seen a poorly balanced prop shake a wind generator to death, vibration like you wouldn't believe, enough to make shrapnel of bearings, brushes & commutator following a day or two of unregulated unstoppable windy RPM.

The eccentric oscilation off a homemade piece of crap will make short work of any but the most bombproof wind generator system. No, a prop is something you buy, not make.

**************Not that I know anything about anything, but wouldn't the number of rotations make up for the smaller dimensions?

Like if you could harness pinwheels, at a cheap cost, but have thousands of them, that would pick up the slightest breeze/belch/fart, isn't it possible that a few could make up for one?**************

Yes to all of that.
Except that you have to have drive efficiencies. That is to say if you hope to extract any work ( energy) from a thing that thing must be able to over come the power depletion inherent in he drive mechanism as well as the work.

Take the Generator: It's a magnetic field spinning inside another. The electricity is created when the fields come into conflict and the power driving the generator is adequate to push the magnets past their points of resistance and then again past their points of attraction.

Take the drive: Bearings consume energy. Pinwheels have none because you expect to throw them away in a matter of hours and not use them to do any work. Bearings consume power, There has to be bearings at the initial dive component ( the pinwheel or fan blades etc.) then more at all of the driven components ( the various gears or pulleys or chains used to transmit the power to the generator) and then each drive component consumes power. V belts are the worst consumers of power Flat steel belts consume the lease.

So between the actual wind and the point where energy is produces there are power consumptions elements that sap the power away.

You need a wind turbine or fan or whatever that has enough power to both oversome all the transmission components drain but then has enough left over to make electricity.

That's why the conventional turbine is huge. The length of the blades is where all that power comes from Ya gotta have a lot of airfoil sticking way out past the center axis ( in engineering terms: this is a moment arm) in order to get the power you need to get done all the things that must get done.