The Irrawaddy (Ayeyarwady) Delta is the low plain of southern Myanmar where the Irrawaddy River splits into a fan of tidal channels. It runs about 290 km from the limit of tidal influence near Myanaung to the Andaman Sea and the Bay of Bengal, and fills most of the Ayeyarwady Region, which covers 35,140 km² and had 6.18 million people at the 2014 census. Much of the land lies only about 3 m above sea level. Rice paddy covers the inland plain, while mangrove and nipa palm grow along the coast, and the delta is Myanmar’s largest rice producer. Its main protected area is Meinmahla Kyun Wildlife Sanctuary, a 500 km² reserve of mangrove forest on an island at the coast. It is an ASEAN Heritage Park and was declared a Ramsar site in 2017. Everything here follows the river’s yearly rise and fall, so this guide follows the delta through one water year.
Where the Water Year Plays Out: Myanaung to Mawtin Point
The delta begins about 93 km above Hinthada. From there the Irrawaddy breaks into its main arms: the Pathein River in the west, the Pyapon, Bogale and Toe rivers further east, and the minor Yangon River on the eastern edge, where Myanmar’s former capital stands. These rivers cut the plain into long peninsulas and islands, among them Haingyi Kyun, Leit Kyun (Turtle Island), Pyin Salu Kyun and Meinmahla Kyun. Two ranges frame the plain: the Rakhine Yoma to the west and the Bago Yoma to the east. The highest point inside the delta is Waphu Mount, which reaches 404 m on the western strip between Pathein and Mawtin Point (formerly Cape Negrais), the south-western tip of Myanmar.
The seaward third of the delta has no relief at all and stretches 130 km from east to west. The sea in front of it is just as shallow. It is less than 5.5 m deep along the coast and stays that shallow for up to 28 km offshore in the east. The rivers carry so much silt that the coast keeps building outward, by roughly 5 to 6 km per century, or about 1,000 hectares of new land a year. Around 3.5 million people live in the delta proper, at about 100 people per km². They are mainly Bamar, Mon and Pwo Karen, in farming and fishing villages and in market towns such as Pathein, Bogale, Pyapon, Maubin, Myaungmya, Labutta and Pantanaw.
February to April: Low Water on the Pathein River
The water year starts at its lowest point. The Irrawaddy is at its lowest in February. Average discharge near the head of the delta drops to around 2,300 m³ per second, against a yearly mean of about 15,100. The cool, dry season that began in mid-October lasts until mid-February. Then the heat builds quickly. At Pathein, the regional capital, the average daily high climbs from 32.1 °C in January to 36.9 °C in April, and the record stands at 41.8 °C. Over the same months the town gets almost no rain: 3.8 mm in January, 7.5 mm in February and 10.2 mm in March.
Without monsoon rain, the low season is when irrigation decides what grows. Rice was once grown only in the monsoon, with the odd pulse crop sown on heavy clay after the harvest. Irrigation now lets farmers grow rice through the year. The dry months are also when weeds and reeds from the channel banks are cut and woven. The mats of Pantanaw are known across the country, and Pathein is known for its parasol umbrellas and its halawa sweet. Because travel in the delta is easiest by water, almost every household owns a boat. Low water is when those boats have the least depth to work with.
Late April and May: Squalls, Cyclones and Nargis
Pre-monsoon squalls arrive in April and early May. The weeks just before the rains are also when cyclones form over the Bay of Bengal. The delta is badly exposed to them because the land is so low and the sea in front of it so shallow. The worst disaster in Myanmar’s recorded history came in this window. Cyclone Nargis formed on 27 April 2008 and came ashore in the Ayeyarwady Division on 2 May at peak strength, with winds of at least 165 km/h on the India Meteorological Department’s measure. Its storm surge pushed 40 km up the delta.
The official count was 84,537 confirmed dead and 53,836 missing, a combined toll of 138,373. Labutta Township alone reported about 80,000 dead and Bogale about 10,000 more, while about 2.5 million people were left homeless. Damage was put at US$15.3 billion, which made Nargis the costliest cyclone on record in the North Indian Ocean until Cyclone Amphan in 2020. The military government at first resisted large-scale foreign aid, which slowed relief. The storm also stripped coastal mangroves and cleared forest, leaving the shoreline even less protected against the next surge.
June to September: 680 Millimetres a Month at Pathein
The south-west monsoon sets in from mid-May, and the delta takes most of its yearly rain in the next four months. Pathein’s records show the scale. May brings 276 mm, then June 604.5 mm, July 682.7 mm and August 681.3 mm. Over a year the town gets nearly 3,000 mm, and almost all of it falls between May and October.
The river rises with the rain and with snowmelt from the far north of Myanmar. Average discharge at the head of the delta reaches about 32,600 m³ per second in the wet season and has peaked at more than 40,000. It is highest in August. Upstream at Mandalay and Pyay, the gap between low water and flood level has been measured at 9.7 to 11.4 m. Down in the delta that water spreads out, bringing the fine silt that renews the paddy soils and keeps the coast moving seaward. It also brings floods. Flooding in July and August 2018 cut Myanmar’s national rice output by about 1.5 percent.
Most of the fields are protected by works from the colonial era. After Britain annexed Lower Burma in the Second Anglo-Burmese War of 1852, the authorities drained the marshes and, from 1861, started building dykes and embankments. Migrants came south from Upper Burma to farm the new land. Today about 1,300 km of major embankments protect some 600,000 hectares of paddy. This is the main rice season. The monsoon crop needs little intervention, and the delta grows nearly half of Myanmar’s monsoon harvest. Ayeyarwady Region alone holds about a third of the country’s harvested rice area.
October to January: Harvest and the Road to Yangon
The rains ease in October, and Pathein’s rainfall drops to 65.9 mm in November and 3.5 mm in December. The cool, dry season runs from mid-October to mid-February. This is harvest time on the plain. Two-thirds of the delta’s arable land is under rice, and yields run at about 2,000 to 2,500 kg per hectare. The crop and the people who grow it move by water. Steamers serve the larger towns such as Bogale, Mawlamyinegyun and Myaungmya. The Twante Canal, dug in the colonial period, links the delta’s channels to Yangon. It is the only large canal in a region with no extensive network of irrigation or transport canals.
That link to Yangon made the delta the base of colonial Burma’s rice trade. The delta became one of the world’s top rice-exporting regions, and just before the Second World War Burma was the largest rice producer in the world. Between 1852 and 1937, roughly 2.6 million people migrated from India to Burma, and most of them settled in the delta and in Yangon. Indian Chettiar moneylenders became the main source of farm credit. Fishing goes on in the same season. Fixed fishing frames and small boats work the channels, and prawn fishing and the gathering of sea turtle eggs are both commercial trades. Both now suffer as mangrove is cleared for more paddy.
Winter on Meinmahla Kyun: Shorebirds and Crocodiles
The dry months bring migrant birds to the mangrove coast. Meinmahla Kyun, an island on the delta’s coast, rises only 0 to 30 m above sea level and is covered by about 40 species of mangrove. Boat surveys in February 2006 recorded 102 bird species, including glossy ibis, bar-tailed godwit, whimbrel and black-crowned night heron. Observers in December 2016 recorded the critically endangered spoon-billed sandpiper, along with Nordmann’s greenshank, Asian dowitcher, great knot, lesser adjutant and brown-winged kingfisher. The sanctuary also holds saltwater crocodiles, 59 fish species, 12 shrimp species and 10 crab species. In February 2016 a camera trap took Myanmar’s first photograph of a fishing cat there.
The dolphin named after the river is not a delta resident. The Irrawaddy dolphin is a coastal and estuarine species that enters rivers. Its best-known Myanmar population, estimated at 58 to 72 animals, lives in a 370 km freshwater stretch of the river far upstream, where it herds fish towards cast-net fishermen. From there the water year comes round again to the low water of February. To follow the same water back to its glacier sources in Kachin State, read our Irrawaddy River guide. To see how the delta fits between Myanmar’s mountain ranges, read our guide to the geography of Myanmar. And to compare its scale with the Ganges–Brahmaputra, Mekong and Nile, see our ranking of the largest river deltas in the world.