Yes, a BIG bummer. It is due to fertilizer runoff way upstream, although less water flow because of the drought no doubt does not help. A big problem is that it is poisoning all the wildlife that drink from the river. They are also warning you to NOT let your pet drink from the river, or even walk into it. If they do jump in, you are supposed to bathe them immediately. It has been well over a year that I was there, but the combination of bad water and the drought has made the deer walking skeletons!
Don't know about the cows. I assume they are upstream? If so, they are no doubt part of the cause.
They are still letting you wade in the water in places, but don't recommend it and no swimming whatsoever!!! I did notice that some of the stores in Springdale are renting "dry bibs" and even "dry suits" for hiking the narrows.
I recall one year in the Zion high country, it was difficult to find a flat area to set up my backpacking tent for the most unusual reason--fawn and small deer carcasses every decent place I could find. But they were all from cougar kills. I have noticed that seeing deer in the high country was rare. I only recall seeing one live one up there ever. A large one. That was in
Telephone Canyon. I had the feeling there were way too many cougars in that area and not enough deer. Well opposite of most places. The only fawns I have seen up there were the dead mostly eaten ones.
Hop Valley is also inside of Zion Park. But it's a hike to get there. best to ignore the sign that says "Hop Valley, Two miles" because they are using map miles, not true miles. That two miles will take most of the day as the trail goes around and over several hills, nothing near a straight line as if on a topo map. IMO, trail signs should be in average time, not miles. Miles is often misleading as it is often done differently at different places. But when way out in the boonies, it is expected the the hikers know what they are doing and know how to read a topo map.
Every time I have been in Hop Valley, I saw MANY cows grazing. I thought that was unusual for a National Park.
-Don- Auburn, CA