A network of marine conservation zones will be created around Britain's coast, the environment secretary has announced.
Hilary Benn explained the zones would help to protect species and habitats of national importance.
They will come into effect by 2012 under the government's draft marine bill.
Certain practices will be banned in the marine nature zones, including some types of fishing and dredging.
Mr Benn announced plans for a new Marine Management Organisation to regulate development and activity at sea and enforce environmental protection laws.
"We have a duty to look after our seas for future generations," he said.
"Our proposals will raise protection and management of our seas to a new level, halting the decline in biodiversity to create clean, healthy, safe, productive and biologically diverse oceans and seas."
The Marine Conservation Society (MCS) has welcomed the proposals but is concerned that the bill in its current form does not make a strong enough commitment to the establishment of an effective network of highly protected marine reserves.
"The piece-meal management of existing so-called 'protected areas' such as special areas of conservation does not adequately protect our valuable marine wildlife," said MCS biodiversity policy officer Dr Jean-Luc Solandt.
"Some of these sites allow practices such as scallop dredging, beam trawling, gillnetting and dredging to damage our marine environment."
Another aspect of the bill - measures to give people the freedom to walk round the English coast for the first time - have also come in for criticism.
The Country Land and Business Association (CLA) claims the plans ignore the losses country businesses could suffer and said farmers would face greater liability for farm animals and buildings not designed for public use in areas where no access previously existed.
"There are far too many unresolved issues to make this workable without riding roughshod over private landowners and coastal businesses," said CLA vice-president Harry Cotterell.
But the Ramblers Association said the greater access is "much needed".
"Improving the legal right to freely access our coastline and beaches will deliver huge benefits," said RA chairman Kate Ashbrook.
"Safe passage of this draft legislation is essential to ensure that this generation can, for the first time, walk around the English coast without hindrance."