Fish can hear you talk, but the fish are not listening to your words and they cannot understand your words.
Sounds travel poorly from air to water, so normal talking above the surface of the water won't scare the fish away, but fish are also very sensitive to vibrations and stomping, dropping things or running a motor will send shockwaves through the water and spook fish.
Fish don't have any external ear flaps like us humans and instead the fish have internal ears that are equipped with special bones that are called otoliths that detect sounds and vibrations.
Fish also feature what is known as a lateral line, which is a series of tiny pores that run along the sides of the fish.
The lateral line that fish have act almost like a radar and allows the fish to feel pressure changes and low frequency vibrations by nearby movement.
And because the air and water also have different densities, the surface tension of the water also acts as a barrier to the sound and most normal human conversation bounces off the surface of the water, although any noise or impact, which happens directly in the water will transmit swiftly.
Fish are also able to see you on the bank as fish eyes are located on the sides of the fish's heads and fish have a massive field of view or vision, which is up to 360 degrees.
Due to the fish's excellent and massive field of vision that is up to 360 degrees the fish can easily spot shadows and movement outside of the water, including on the bank.
Fish can see you through the "Snell's Window" Effect and distance.
When it comes to the "Snell's Window" Effect, due to the way the light bends (refracts) in the water, the fish can actually see you even when you're sitting far back from the water's edge.
The fish look up through a cone shaped window in the water's surface and see a distorted panoramic view of the sky, the trees and yourself and others.
Most freshwater fish are also near sighted and can see around 15 feet in front of them with great clarity.
Although if the water is clear and calm, the fish can also easily spot a human that is standing high on a bank from further away.
To avoid the fish seeing you and help yourself remain hidden when fishing, watch your silhouette and avoid standing directly on the skyline or on the edge of the bank, as it creates a highly visible silhouette of yourself.
And wear earth toned colored clothes, as bright colored clothing creates a stark contrast against the natural background, wear greens, browns or camo to blend in.
And avoid making any sudden movements, as any quick, jerky movements will spook fish much faster than simply remaining standing still.
You can also use natural cover, like trees, bushes, or tall grass along the shoreline to break up your profile.
Also making noises and talking too loud can even spook fish, so you need to remain somewhat quiet, although talking in normal volume is okay.
Fish can hear sounds, but they can't hear the specifics of your conversation, and so having a casual conversation won't send the fish fleeing in terror, but making any loud or sudden noises will spook fish.