bulbeop tugi ttaemune hacheoni oyeomdoeeossseupnida.

Yes, 투기 can mean different things depending on context.

In 불법 투기, it means illegal dumping or illegally throwing away waste.

That is different from the 투기 meaning speculation, as in financial speculation.

So in environmental contexts:

• 쓰레기 불법 투기 = illegal dumping of trash
• 불법 투기 때문에 = because of illegal dumping

Context tells you which meaning is intended.

때문에 means because of or due to.

It attaches to a noun phrase, so:

• 불법 투기 = illegal dumping
• 불법 투기 때문에 = because of illegal dumping

This is very common when giving a reason or cause.

A useful pattern is:

• Noun + 때문에 = because of noun
• Verb stem / adjective stem + 기 때문에 = because verb/adjective

Examples:

• 비 때문에 늦었어요. = I was late because of the rain.
• 아프기 때문에 못 갔어요. = I couldn’t go because I was sick.

Yes. 때문에 often sounds neutral-to-negative, and it is very commonly used when the result is bad or unfortunate.

That makes it a very natural fit here, because pollution is a negative result:

• 불법 투기 때문에 하천이 오염되었습니다.

If the cause leads to a good result, Korean often prefers 덕분에:

• 도와주신 덕분에 일을 끝냈어요. = Thanks to your help, I finished the work.

So 때문에 is not wrong for all situations, but it often feels especially natural with problems, blame, damage, inconvenience, and so on.

In this sentence, 하천이 is the thing that ended up in the polluted state, so it is marked as the subject.

• 하천 = stream / waterway / river channel
• 하천이 = the stream/waterway as the subject

The sentence is structured like this:

• 불법 투기 때문에 = because of illegal dumping
• 하천이 = the stream/waterway
• 오염되었습니다 = became polluted / was polluted

So the stream is not marked as an object here, because the verb is 오염되다, not a transitive verb like to pollute something.

Great question. 오염되다 is the usual verb for to become polluted / to be polluted.

It is built from:

• 오염 = pollution, contamination
• 되다 = to become / to come to be

So:

• 오염되다 = to become contaminated, to be polluted

That is why 하천이 오염되었습니다 means:

• the stream became polluted or
• the stream was polluted

If you want to say that someone or something polluted it actively, Korean often uses 오염시키다:

• 공장이 하천을 오염시켰습니다. = The factory polluted the stream.

So:

• 오염되다 = intransitive / passive-like result
• 오염시키다 = transitive, actively causing pollution

오염되었습니다 is past tense and formal polite style.

Breakdown:

• 오염되- = verb stem
• -었- = past tense
• -습니다 = formal polite ending

So it is the kind of style you would see in:

• news reports
• public announcements
• official writing
• formal presentations

Less formal versions would be:

• 오염되었어요 = polite
• 오염됐어요 = polite, contracted and very common in speech
• 오염됐어 = casual

It can match either one depending on context.

Korean 오염되다 often focuses on the resulting state, so English may translate it as:

• became polluted
• was polluted
• has been contaminated

In this sentence, both became polluted and was polluted are reasonable.

A learner should remember that Korean does not always divide these ideas in exactly the same way English does. The important point is that the stream ended up polluted.

하천 is a somewhat formal word meaning stream, waterway, river channel, or more broadly watercourse.

It is often used in:

• environmental discussions
• government or legal language
• news reports
• geography-related contexts

It is not always exactly the everyday English word river.

Related words:

• 강 = river
• 개울 = brook / small stream
• 하천 = a broader, often more formal term for a waterway

So 하천이 오염되었습니다 sounds a bit formal and fits well in an environmental or official context.

Yes. In everyday conversation, people would often use a less formal ending:

• 불법 투기 때문에 하천이 오염됐어요.

This means the same thing, but sounds more natural in normal spoken Korean.

If you want to sound even more conversational, the exact noun might also change depending on the situation:

• 강이 오염됐어요. = The river got polluted.
• 개울이 오염됐어요. = The stream got polluted.

The original sentence is perfectly natural, but it sounds more formal and official.

Korean word order is somewhat flexible, so you can move parts around more than in English. But the most natural order is often:

cause/reason + subject + verb

So:

• 불법 투기 때문에 하천이 오염되었습니다.

You could also say:

• 하천이 불법 투기 때문에 오염되었습니다.

That is still understandable, but the original version sounds smoother and more standard, especially in formal writing.

Putting the reason first is very common because it sets up the cause before giving the result.

Yes. A common formal alternative is 으로 인해 or 로 인해, which also means due to or because of.

For example:

• 불법 투기로 인해 하천이 오염되었습니다.

This sounds very formal and is common in reports, announcements, and news language.

A rough comparison:

• 때문에 = because of, due to
• 으로 인해 / 로 인해 = due to, as a result of, because of

Both work here, but 으로 인해 can sound even more formal or written.

Because this sentence is not using a transitive verb that takes a direct object.

The verb here is 오염되다 = to become polluted / to be polluted.
That means the stream is the subject of the change in state:

• 하천이 오염되었습니다. = The stream became polluted.

If you use a transitive verb, then you would have an object:

• 누군가 하천을 오염시켰습니다. = Someone polluted the stream.

So compare:

• 하천이 오염되었습니다. → subject marker 이
• 하천을 오염시켰습니다. → object marker 을

That difference is very important in Korean.