I've done upper Fish Creek probably 7 times now but never went downstream from the bridge so Saturday I did. I started before 7:30 with no real stopping point in mind. Since it was just me I went in until I'd had enough and found a nice swim spot, which happened to be around 4.4 miles in (just after the awesome camp spot). Lower's much different than Upper in that it receives more sunlight and has no real bouldering. No large rock traffic jams created hardly any deep swim spots though. I'd say this end is much more scenic but I do like the choose your own adventure challenges of upper. I kept my feet dry for too long on the way in which made going a little slower fighting the brushier banks. After my turnaround spot and the um... unfettered swimming and waterfall jumping, I stayed in the water hiking back and made better time.
I didn't get to see any of the coatimudi or mountain lions others have mentioned, just the basic beautiful scenic stuff. However, I did have my first shady backcountry encounter where I believe things could have gone bad. About 1.5 miles in (almost 2 creek slogging/rock hopping hrs in) I encountered a group of 4 hispanic males who appeared to be setting up camp. Our quick exchange was cordial enough. My mind later asked how often do you encounter groups of non-white hikers in the middle of nowhere- More of a Things-white-people-like than a pointed racist thought. On my return hours later I heard a loud motorized noise as I approached where I had seen them. By the time my mind let go of it being a chainsaw, their scout had seen me and tried to hurriedly motion for the others to shut it down. This time as I passed, they said no word. I said "How's it going," with no response as I kept moving. I could not resist temptation to glance once back where they were all popped up now staring at at me tensely from what I can only suppose as their now stopped illegal drill/mining work? I did worry about the back of my head until I could round a bend. I'm sure they saw my side arm and extra mag on my backpack strap as I had passed the first time but there were four of them so... Suspicions were further aroused when I inspected their vehicle to find a note conveniently placed over the VIN stating "Car will not start, be back to fix."