The Stream Doctor

January 10th, 2005

Email YOUR Questions directly to the Stream Doctor. This is your opportunity to get an experts professional opinion on anything stream related.

Q. My question concerns a trout's field of vision. On limestone trout streams, brown trout are tough to catch because they can see you before you see them. How far in front and how far in back can a trout see? I have spooked trout even when approaching from behind like the book says to do. Nothing I do seems to work except to fish very early or late in the day when there is not much light. Thanks for any reply.

A. You've broached a complicated subject; the subject of how a fish sees takes up over 10 pages in one text I have. I'll try to simplify it to get at what you are interested in.

A trout looking upward, we'll assume straight up, can see through a circular area that is bounded by the angle at which light is refracted back into the water from the surface. This angle is roughly 45o from the vertical and thus about 90o in total. The size of this circular window increases with depth, so a fish in 5' of water will have a larger window than one just under the surface.

That tells you how much of an area a trout can see through, but doesn't tell you how far to the sides it can see. You are familiar with the way that light rays bend in water; things aren't where they appear because of this refraction. The same thing happens in reverse for the fish. Light rays bend away from the edge of their circle of vision; thus, they can see objects that are outside of the "line of sight" from their eye to the edge of the circle.

Unfortunately, we can't see this circular window to gauge how far to stay back or down. The only rule of thumb is that the closer you are to the vertical above a fish, the more likely it is to see you and the lower and further back you stay, the better chance you will have of not being seen.

One other point you alluded to. Even when staying low and behind objects, don't forget that a fish can be spooked by senses other than sight. Most importantly here is the lateral line on the sides of fish. These nerve endings are sensitive to pressure changes resulting from such things as heavy walking or jostling of rocks on the stream bottom. These can send a fish away just as sure as a visual sighting.

If you have a question, please feel free to contact me.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to anything stream related directly to him for use in this Q & A Feature at

If you would like to comment on this or any other article please feel free to post your views on the FAOL Bulletin Board!

Previous Stream Doctor Columns

[ HOME ]

[ Search ] [ Contact FAOL ] [ Media Kit ] © Notice