A four-week public inquiry has begun into plans for a £100m flood barrier scheme in Lincolnshire.
The creation of the Boston Barrier would help to reduce the risk of tidal flooding for up to 14,300 properties in the town, the Environment Agency said.
The inquiry will consider its environmental impact and benefits.
Some fisherman claim the barrier's proposed location would narrow the river at that point, making it riskier for boats to navigate safely.
The Environment Agency will use the inquiry in Boston to put forward its case and to hear evidence about these and other objections raised.
Last year it asked the secretary of state to grant powers to construct and operate the proposed barrier, which led to the public inquiry being called.
Adam Robinson, barrier manager for the agency, said the scheme was needed to prevent a repeat of the 2013 floods, which saw about 300 homes flooded after a tidal surge battered the east coast.
Ken Bagley, from the Boston Fisherman's Association, said while he supported a barrier in principle, in his view the proposed site was incorrectly positioned.
He said narrowing the river at the point, along a busy stretch and on a bend, would increase the speed of the water passing through it, meaning boats would have to travel at higher speeds to navigate it.
Mr Bagley said the barrier should be built downstream to avoid the bend.
A government inspector will be present for the inquiry and will prepare a report for the secretary of state to consider.
If approved, the scheme would see the construction of a new tidal barrier with a moveable gate, along with new flood defences on both banks of the River Haven.
Work could start in December and was estimated to take about two years to complete, the agency said.