Looks like a very good start -- your rocks and that dead treetrunk are really pretty good. You might want to find some photo references for water... it looks like maybe you're trying to guess what it would look like.
Luckily, Mr. Internet is your friend here :-) Specifically, I recommend going to the Flickr Search page and searching for something like 'stream'. I always click the "Only search within Creative Commons-licensed content" button to make sure I'm playing nice.
You can find things like this picture or this picture -- images like that should help a lot.
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