China has banned commercial fishing for three months along a 1,000km (620 mile) stretch of the Yangtze River in a bid to protect threatened fish stocks.
Fishing boats will be banned from trawling in central Hubei province and Chongqing Municipality, according to the official Xinhua news agency.
Bans covering two other stretches will take effect from April.
The government says it has imposed the bans to make sure that stocks of fish are not wiped out.
But a BBC correspondent in Beijing says hundreds of fishermen will have to find another way to earn a living while the bans are in place.
Controlling and monitoring the state of the Yangtze - and what is in it - has been a central concern of Chinese leaders for many hundreds of years.
Environmental experts accuse the government of failing to keep the river clean.
They say that industrial waste and sewage have made the river seriously polluted.