More than 800 sightings of whales, dolphins and seals have been recorded in British waters this year.
One project saw 320 whales, dolphins and porpoises spotted off the Yorkshire coast, conservationists said.
And 483 grey seals including seven pups were recorded in Cumbria, a 34% rise from last year.
The Wildlife Trusts said there had been "a sea-change in people's attitudes" but UK waters were still at risk from invasive species and plastic rubbish.
The organisation is a combination of 46 individual wildlife trusts around the country, each of which are charities run by members and volunteers.
The Yorkshire project saw trained citizen scientists recording hundreds of individual sightings.
More grey seals have been reported than ever before at South Walney nature reserve in Cumbria - with 483 seals including seven pups, up from 360 the previous year
Photographs captured a pod of bottlenose dolphins travelling from Scotland to Flamborough Head in East Yorkshire, the furthest south they had been officially identified.
Bex Lynam, North Sea Wildlife Trusts' marine advocacy officer, said: "It's likely the bottlenose dolphins came south following shoals of fish; it's thrilling to see playful dolphins and ocean giants like whales.
"Ten years ago, seeing a bottlenose dolphin off the Yorkshire coast would have been rare.
"We need to collect more data about how and why they are using these waters if we are to better protect them."
Researchers also logged minke whales feeding off Staithes, in North Yorkshire.
Cumbria Wildlife Trust said it had reported more grey seals at South Walney nature reserve than ever before. Last year it had recorded 360.
A seal was also discovered commuting between the Isle of Man and Cornwall, revealing for the first time how far seals would travel for food and a place to have pups.
Plastic rubbish is mistaken for food by marine wildlife and is a danger to animals, the Wildlife Trusts says
Photographs sent by the Manx Wildlife Trust to the Cornwall Seal Group revealed the animal, nicknamed Tulip Belle, has been a regular visitor to the South West since 2001, returning to the Calf of Man to have pups every couple of years.
Joan Edwards, The Wildlife Trusts' director of living seas, said "more people than ever" were volunteering to help the coast, amid growing concern over wildlife, climate change and pollution.
But the trusts said wildlife was "increasingly being disturbed by people" including people on personal watercraft frightening dolphins and kayakers scaring seals.