Fire, police and coastguard teams were called to Butley Creek near Orford, Suffolk, on Wednesday by a member of the public who had seen the supine figure of a man lying in the water.
The "body" turned out to be a work of art called A Thousand Tides, which has been at the site for more than a year.
A Suffolk Police spokesman described the work as "quite realistic".
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The sculpture, by artist Laurence Edwards, was designed to only be seen at low tide and was intended to sink eventually.
However, Mr Edwards said it had "stayed on the surface longer than it should".
He said: "I've always been a bit worried that a helicopter would spot it and want to rescue it.
"To convince someone it's a real person is a great achievement, although I would like to apologise to the poor person who called it in."
The sculpture was a parting gift to the area from Mr Edwards, who had a studio and foundry works nearby for 15 years until spring 2016 before moving to Halesworth.
Mr Edwards' website says his work "attempts to do justice to the locality and its history, by peopling it with large figures that have survived the ravages of the water and the elements."
Suffolk Police confirmed they attended Butley Creek, saying: "Police received a call from a member of the public reporting what they believed to be a body in the river.
"The fire service and coastguard were also called to assist, but a short while later this was actually confirmed to be a sculpture."
A Thousand Tides is reminiscent of Antony Gormley's Another Place installation on Crosby beach in Merseyside, which depicts 100 bronze figures looking out over the Irish Sea.

Powell, 22, scored 12 goals in 41 appearances for Championship side Wigan during a loan spell in 2013-14.
He joined United for £3m from Crewe in 2012 and was loaned out to Leicester City and Hull City before his contract expired in June.
"He is the one player we wanted this summer and we are so happy we've got him," said Wigan boss Gary Caldwell.

Stormont officials have refused to give any details citing confidentiality.
Homeowners will not face bills until at least March 2017, after MLAs ruled to defer charges.
Instead, the executive pays the cost of Â£280m a year to NI Water. Further legislation is expected to extend the policy.
However, the decision could mean that the authorities are not complying with European rules on water quality.
The EU Water Framework Directive envisages that users should pay for their water to promote conservation.
Officials in Northern Ireland make the case that people do that through their regional rate.
Northern Ireland is the only part of the UK not to levy a charge on homes, although businesses do pay charges.
That has prompted a debate with calls for the introduction of a charge on homes to pay for improvements in infrastructure.
Now, the European Commission has opened a so-called "pilot case" to look at the issue.
Essentially, this is a way for the commission to establish whether EU rules are being correctly applied.
It allows for the commission and member states to resolve any conflicts without resorting to infringement proceedings.
The Department of Agriculture Environment and Rural Affairs (DAERA) said it could not comment on the detail of the case.
"It is the subject of a confidential dialogue with the Commission and the release of further details could potentially prejudice the outcome of those discussions," said the department.
The two sides get about 20 weeks to try and sort out their differences.
Many cases are resolved without going to a formal hearing.
Three different 999 services had to be stood down after a "body in the water" turned out to be a bronze sculpture.
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Wigan Athletic have signed former Manchester United midfielder Nick Powell on a three-year contract.
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The European Commission has asked questions about the Northern Ireland Executive's decision not to charge homeowners for water.