Ever spot a fish and just for the learning experience, see how close you can get before it spooks and heads off into a safe place? I have gotten to within a couple feet of some fish, and spooked others when 50 ft away. A number of things seem to come into play here. For example is how visible are you, and how threatening do you appear? Does sound contribute to the problem?
If there is a wind and there are ripples on the water, your visibility to the fish will be diminished. So when approaching a 'fishy spot', think about coming in from down wind and you will get closer without being noticed. Also note that your height will make you more visible. So keep a low profile and if possible keep the sun in front of you so your shadow doesn't give you away. Not only the shadow of yourself, but also that of the boat, and your rod as you cast to the fish.
I fish a lot out of an electric powered kayak and often use a paddle to assist while exploring for new fishing sites. Using a paddle I can reduce the power setting of the motor and almost double the range of the boat while maintaing a 3-3.5 mph cruising speed ( a bit over walking speed). In the summer the fish like to sun themselves near the surface of lakes. As I move along and I can see their swirls as they are alarmed by the approaching boat. It is surprising how quickley they become spooked when using the paddle, streaking off while still 50 feet in front of me. On the other hand, if I just let the breeze move me along and leave the paddle in its cleat, the fish will not run until the boat is just a few feet away. Part of this is because the boat is moving slower, and is not as threatening. Also if I use the motor for power, even at cruising speeds I can get much closer to the fish without the paddle. Those flashing paddle blades are like waving a flag that you are approaching and you are armed.
I have noticed the same affect on wildlife. Deer along the bank of the river are not alarmed if I do not use the paddle. The other day I came across a family of otters. Using the electric motor and moving slowly I found they were more curious about the boat than afraid of it. The younger otters swam out to get a better look at the craft and came to within 10 ft of the boat before deciding it was too big to play with. On another occasion a salt water otter swam over my way and dove swimming on his back under the boat so as to get a good look at it. He came up on the far side and looked a bit longer before swimming off. A small boat with no paddle action is not very threatening to wild life. In a past blog I describe how a couple of sea lions trashed my steelhead fishing spot, often coming to within a few feet of the boat. So you get to se a lot more if you maintain a non-threatening profile in the wild, sometimes a little more than you want.
How about noise? When fishing trout in Arkansas with my Bro, we drifted down the White river dragging a heavy chain to slow the boat. We caught lots of fish and no effort was made to be stealthy. Yet on many occasions I have spooked fish with just a tap on the hull of the boat. What is the difference here? Well I think the fish on the White have come to accept the dozens of chain dragging boats that pass every day as "normal", and non-threatening. They might even interpret the chain as the dinner bell, drawing closer to the passing boats. Perhaps it is all in what they get used to. Heavily fished waters are probably more tolerant of fishing activity than those that do not have many boats on them. So to be on the safe side, I usually move along quietly. However I have no concerns about chatting with a fishing partner in another nearby kayak. The noise level above the waterline doesn't seem to bother the fish, but it sure can be annoying to fishermen. Good fishing and paddling!