Also know as Great lobelia. The water is down in the creek so I took a look for rocks and arrowheads. I found these growing along the banks, altho not many. It can grow 3 ft and comes in colors of light or dark violet, light or dark blue or lavender, rarely white.
Plant contains a narcotic poison and was used in medicine.
Heres a link for more info Blue lobelia
Sometimes the little beauties of nature might be in the garden or along a creek bank, always keep looking.
Have a great week , Autumn is in the air : )