SWANSEA West MP Geraint Davies has voiced misgivings about the proposed Swansea Bay tidal lagoon.
A formal consultation is currently taking place about the £650million-plus structure which, if given consent, would take shape between the Rivers Tawe and Neath and extend into the bay.
Mr Davies said his view could change if his visual impact and environmental concerns were addressed by developer Tidal Lagoon Swansea Bay.
"We need to make a considered judgement on how this will affect the iconic view of Swansea Bay and our ambition to become a quality tourist destination and UK City of Culture," said the Labour MP.
"Changing our view of Swansea Bay will change our identity for ever. This is an historic choice for Swansea so let's make it with our eyes open with our long-term interests in mind."
The bay, he said, was "our biggest natural asset to attract inward investment and tourism, so we should think twice before changing it for green energy".
He added: "Efforts have been made to ensure the lagoon would have rock cladding to improve its appearance but this wall would 'rise' up at low tide. Visitors and residents may prefer an open sea view."
Mr Davies said he also felt an ongoing share option for local residents could end up resulting in pressure being applied on local AMs and MPs to support the lagoon proposal. He said local investors could expect to earn nearly £3,800 for an £800 share if consent was granted.
A decision on the scheme will, however, be made by the UK planning inspectorate once a development consent application has been submitted by Tidal Lagoon Swansea Bay.
Mr Davies also claimed that potentially toxic waste in the seabed could be disturbed during construction, adversely affecting the bay.
A Tidal Lagoon Swansea Bay spokeswoman said company representatives had already met Mr Davies and would write to him to try to allay his concerns.
She said the MP, plus other individuals and groups, had copies of the company's preliminary environmental information report, which examines 16 subjects, including the lagoon's impact on coastal processes, water quality and ecology.
She said: "Further studies are ongoing and more detailed analysis will be published in our full environmental impact assessment later this year where Mr Davies's queries will be answered in depth, and which will steer our final designs and construction methods."
The spokeswoman added: "We want to make sure that local people are given the opportunity to have their say and to tell us what they would like to see — we want the lagoon to become a local icon that is of benefit to local residents, the economy and the tourism industry here in Swansea, while creating jobs and generating significant amounts of renewable power."
The planned lagoon will, it is said, create enough electricity to power 121,000 households, with its construction cost borne by private investors. Government-backed subsidies will help generate a return.
Referring to the share option, the company spokeswoman said: "Over 400 local people have registered their interest in investing and all are fully aware that this is for early stage development investment and therefore high risk. That is exactly why the potential returns are so attractive, but in no way do we believe that this could apply pressure to any local representative."
Hundreds of people have been attending local exhibitions about the lagoon, with some 1,700 questionnaires returned.
Events take place today at Baglan Community Centre, Hawthorne Avenue, Baglan, from 3pm to 8pm, and on Friday and Saturday from 10am to 5pm at Princess Royal Theatre, Port Talbot.
Asked for her thoughts on the lagoon, Swansea East MP Sian James said: "A clean renewable energy project of this kind is a fitting element in the transformation of Swansea's docklands.
"I have another meeting scheduled with the company in the next few weeks and I expect to be briefed on all the environmental safeguards."