First thing you need to know is this is NOT your problem. Do not and I repeat do not mess with that creek. The government will fine you depending on your State. There are 'buffer' zones associated with ALL creeks, now and they will get you on what ever you are doing within that buffer zone.
Find out what your State or County's rules are for riparian systems, surface water systems, watersheds, lakes and wetlands. We had salmon creeks in the Northwest that were vigilantly monitored. 600 foot buffer zones on salmon creeks; no fertilizer for a lawn for example, no dumping anything into that creek, no construction whatsoever within the buffer zone and absolutely no adding bank protection or making riffles or planting plants within that zone. Whatever municipality's department that is responsible for that creek are the ones PAID to do that work, licensed and monitored by the government. And you could get in trouble because you don't know the rules. No one other than the municipality 'owns' rivers and watersheds. They don't own them either, they are just the ones charged with proper care as just one mistake upstream could harm everything down stream.
Start out being anonymous when you call your Buildings and Code department as well as the water department or any of the government offices. The best people to call would be your Cooperative Extension Service. They know these rules and help others comply. And they won't fine you for something you had no idea about...
In fact, the riparian and surface water departments will love you for bringing this to their attention when you know more. Later on make sure you are there when 'officials' come to your site. Make sure that NO ONE adds any pesticide without a current pesticide license to include water treatment. One needs a special license to use pesticides in any water systems or wet lands. Make sure someone has that license.
If you live in the states, I doubt you can call this creek 'yours'...like roads, drives and easements, you should get to know the 'rules' of this surface water system. It should be in your mortgage paperwork! Your neighbors should know this stuff. I am sure you could find this information on the internet for your...county? Perhaps City usually county. I'd find out the laws first before talking to anyone in the government.
This is where your closest big University (name) Cooperative Extension Service is helpful! They will educate you and give you proper directions on how to proceed. They will tell you whose responsibility it is, provide phone numbers, names. Please let us know what you've learned when you make a few calls!