There are very safe effective treatments that can be successful. I'm guessing this Creek is fairly cold and if the trout have been surviving then I wouldn't get crazy changing put fish quite yet. Take a comprehensive look at the big picture with your pond.
What would some of the "effective" treatments be in a pond with constant flow? Any chemicals will be flushed out and kept diluted, and fresh nutrient is constantly introduced.
The ONLY safe and effective treatment I would consider is had by calling Applied Polymer Systems, sending them a water sample to be analyzed along with your desired goals, and they will give you a special blended "log" to put into the inflowing water. It dissolves and binds up the phosphorus needed to take away an essential algae producing nutrient. The logs are not exactly cheap, dissolve in about a months, and require several logs, in stages, to work well.
