Campaigners have called for the bill to offer greater protection to seals
Environmental groups have called on all parties in the Scottish Parliament to strengthen the Marine Bill, which will be debated in Holyrood later.
The proposed legislation, which would set up a marine planning system, will be the subject of a Stage 1 debate.
A report on the bill by the rural affairs and environment committee report said there was a lack of detail.
Groups like the RSPB and Link, a body which includes the Scottish Wildlife Trust, said it does not go far enough.
The report by the Holyrood committee said most of the Marine (Scotland) Bill is intended to "fill something of a policy vacuum in the governance of the Scottish marine area, rather than replace existing law".
It said groups giving evidence to the committee broadly welcomed the proposed law, but that "most also expressed some concerns".
"Most of these have arisen from uncertainty as to how it would be implemented," it said.
"On a number of significant matters, such as the membership of marine planning partnerships or the details of marine licensing, the Scottish government has candidly stated that it has not yet come to a concluded view.
"Whilst this candour is to be welcomed, it has given rise to uncertainties as to the future direction of policy, with one respondent to the committee's call for views remarking that "the lack of detail makes it genuinely difficult for consultees to analyse and comment on the proposals in many areas that could be of critical importance"."
"This has been the committee's experience as well, which, at times, has limited our ability to analyse the bill's likely impact."
RSPB Scotland said there was still room to strengthen the legislation.
Its marine policy officer, Rory Crawford, said: "The Scottish government are rightfully proud of the strong, world-leading climate change act passed this year.
"Given that the basis of this strength comes from the duties placed on ministers in the act, we believe the Scottish government should now show the same ambition with the Marine (Scotland) Bill.
"They can achieve this by creating a network of Marine Protected Areas and producing a coherent marine plan, with clear and ambitious targets as well as policies and programmes to deliver these targets."
Scottish Environment Link, an umbrella body representing 34 environmental organisations, said Scotland's seas would have "a much better future" if parliament developed the legislation.
Calum Duncan, convener of its marine task force, said: "We strongly welcomed the rural affairs and environment committee report and agree that this legislation must go further than was originally proposed.
"It must, like the Climate Change Act, be aspirational and seek to improve the quality of our marine environment for the sake of coastal communities, wildlife and the marine economy.
"Merely protecting what is left in the damaged seas we have created is not good enough."
However, some islanders have warned the proposed legislation could restrict fishing and other developments.
Hugh Douglas, from the Barra Action Group, told BBC Scotland's Good Morning Scotland programme: "It's an absolute power, once these designations are in place you cannot get rid of them.
"Anybody, especially of an environmentalist nature, can put in stipulations and go to Europe and local people have got no come-back, there's no social or economic factors taken into account."