What are the main sources of underwater noise?

In one line

The rule

Underwater noise pollution is caused by natural and human-made (man-made) sounds in water that can disturb or harm aquatic life.

Let's understand it simply

Imagine you are swimming in a pool and someone taps two stones together underwater. You hear a loud clinking sound, even if you are far away. Sound travels faster and farther in water than in air. Now, think about the sea or a river. There are many things making noise under the surface. These noises can come from big ships, machines, or even animals like whales and dolphins. Just like loud sounds can disturb us, these underwater noises can disturb fish and other sea creatures.

How it works

1. Ships and boats move through water, and their engines and propellers make a constant rumbling noise.
2. Oil and gas companies use machines called air guns to search for oil under the sea. These air guns make very loud blasts.
3. Construction in water, like building bridges or ports, uses pile drivers (machines that hammer large rods into the ground), which create strong banging sounds.
4. Military submarines and ships use sonar (a system that sends out sound waves to find objects), which creates loud pings underwater.
5. Natural sources, like earthquakes or underwater volcanoes, also make noise, but most underwater noise today comes from human activities.
6. Animals like whales, dolphins, and some fish make sounds to talk to each other, but these are usually not harmful unless they are very loud.

The story behind it

Scientists first noticed underwater noise when they used underwater microphones (called hydrophones) during World War II to listen for enemy submarines. After the war, researchers found that the oceans were getting noisier because of more ships and machines. In recent years, scientists have studied how this noise affects sea animals. One famous case was when whales got stranded on beaches after loud sonar tests by the navy. This made people realize that underwater noise can be a big problem for marine life.

Where you see it in real life

• Large cargo ships travelling between Mumbai and Dubai → Their engines and propellers create a constant, low rumble underwater.
• Oil drilling near the coast of Gujarat → Air guns used to search for oil make loud blasts that travel far in the sea.
• Bridge construction across the Ganga → Pile drivers hammering rods into the riverbed create strong, repeated bangs.
• Indian Navy using sonar to find submarines → Sonar sends out loud sound pulses that can disturb whales and dolphins.
• Fishing boats using echo sounders in Kerala → These devices send sound waves to find fish, adding to underwater noise.
• Natural events like an underwater earthquake in the Andaman Sea → The quake creates a sudden, loud noise underwater.

Why it matters

• Underwater noise can confuse or scare fish, making it hard for them to find food or avoid danger.
• Loud sounds can damage the hearing of whales and dolphins, or even cause them to get stranded on beaches.
• Many sea animals use sound to talk, find mates, or travel. Too much noise can break their communication.
• Fishermen may catch fewer fish if noise drives them away, affecting their income.

Worked example

Let's see how far a ship's noise can travel underwater:

Given: Ship engine noise = 180 dB at 1 metre
Step 1: Sound loses about 6 dB every time distance doubles
Step 2: At 2 metres: 180 - 6 = 174 dB
Step 3: At 4 metres: 174 - 6 = 168 dB
Step 4: At 8 metres: 168 - 6 = 162 dB
Step 5: Continue doubling distance and subtracting 6 dB each time
Step 6: Even at 1 km (1000 metres), the noise can still be loud enough to disturb whales

Common mistakes

• Thinking only animals make underwater noise. Most noise today comes from human activities like ships and machines.
• Believing sound does not travel far in water. In fact, sound travels much farther in water than in air.
• Ignoring small boats. Even small fishing boats with engines add to underwater noise.
• Forgetting that natural events (like earthquakes) also create underwater noise, but these are less common than human-made sources.

Remember it

Ships, machines, and animals all make underwater noise, but humans are the main source today.