The 40-year-old was swept away while taking the photograph beside a river swollen by the breach of the earthen dam near the southeastern city of Jiroft, a Red Crescent official told the official IRNA news agency.
His body has yet to be recovered.
The dam burst flooded parts of Jiroft, damaging dozens of homes.
A second man was killed in a flash flood in the southwestern province of Bushehr.
The torrential rain caused flooding across the south, from Khuzestan province on the Iraqi border to Sistan-Baluchistan province on the border with Pakistan.
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Thousands fled villages downstream from dams fearing collapses like that in Jiroft.
In the north, at least five people have been killed in avalanches over the past two weeks as up to two metres of snow fell in the Zagros and Alborz mountains.
Hundreds of villages were cut off in the provinces of Kurdistan, East Azerbaijan and Gilan.
Even as downpours gripped much of the south, residents of some areas near the Iraqi border were praying for rain as some of the worst dust storms in years sent hundreds to hospital with respiratory problems.
Photographs shared on social media showed cars, kitchens and furniture caked in thick dust beneath an orange sky.
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The dust level in the air was 18 times the normal levels, officials in Khuzestan province said.
Long power cuts hit the cities of Ahvaz, Khoramshahr and Abadan as the combination of the dust and up to 98% humidity played havoc with the electricity grid.
In Ahvaz, residents held demonstrations calling for government assistance. Several artists and celebrities launched a solidarity campaign on social media.
Some 50 members of parliament have also written to President Hassan Rouhani in support of the campaign.
Weather is getting freaky
Freak weather has swept though much of the Gulf, normally renowned for its deserts and searing heat. Snow fell in the hills of the United Arab Emirates as high winds forced the cancellation of a stage of cycling's Tour of Dubai.
This week torrential train disrupted every day of the Qatar Open women's tennis tournament.
The seasonal dust storms in southwest Iran have been intensifying for years as prolonged drought has triggered increasing desertification, not just in Iran but also in neighbouring Iraq and in Saudi Arabia beyond.
Khuzestan province hosts many of Iran's largest oil fields but its large ethnic Arab community has long complained that the government has not invested enough in infrastructure or measures to tackle chronic air pollution.
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