In a report published today, RenewableUK also says UK ministers' policies could hit the Scottish Government's plans to make the technology central to its ambitious renewable energy targets.
And it accuses the flagship Edinburgh-based Green Investment Bank of failing to prioritise the sector.
RenewableUK estimates wave and tidal energy could be worth £6.1 billion to the UK by 2035, creating nearly 20,000 jobs – up from today's 1000.
The group is holding a conference on the issue in London which will hear from Coalition minister Greg Barker and Scottish minister Fergus Ewing.
The Scottish Government is committed to generating 100% of Scotland's electricity consumption from renewables by 2020.
Ministers have pointed to marine energy as a key part of this drive. But the RenewablesUK report warns those plans could be put at risk by the Tory-LibDem Coalition's policies.
It says the UK's wave and tidal energy industries will only be able to grow if they get the right level of UK Government support.
Without such investment Britain risks surrendering its world lead in marine energy, the study warns.
It points to the largest shake-up in the energy sector for decades, the Coalition's plans for electricity market reform, designed to provide predictable revenue streams.
It warns this faces high risks – and could either act as a springboard for growth or undermine investor confidence in marine power.
RenewableUK's wave and tidal manager, David Krohn, said: "The world's leading projects are being developed in the UK waters thanks to a comprehensive package of support granted by the UK and Scottish governments, which has ensured the UK leads the world in tidal energy. However, there are significant hurdles that need to be overcome to ensure the sustained growth of the industry.
"It's time to get real about the potential risks so we can work with Government and others to find the solutions as early as possible."
A Scottish Government spokesman said: "The UK Government must follow Scotland's lead and give industry the certainty it needs."
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