The event was kicked off on Friday afternoon when supporters of the reserve were invited on a Saltmarsh Safari guided walk with senior site manager John Badley, as well as a second guide on how the team use cows and other techniques to increase bird populations, with site manager Toby Collett.
People were also invited to design and print wildlife artwork that will help form a new metal sculpture celebrating the birds of The Wash by artist Jeni Cairns using a plasma cutter on steel drums. She demonstrated her skills throughout the weekend.
Visitors over the weekend could also sketch nature in a bird drawing workshop based in one of the hides or join in a Cyanotype Workshop using light sensitive paper and natural objects to create images.
There were drop-in writing activities to record your experiences of the landscape, willow weaving, or whittling a swallow or fish, under the guidance of Boston and South Holland Wood Carvers.
Childrens activities included bug hunting, bird spotting, face painting, walks and talks on the wildlife and history of the marsh.
John Badley said 40 years is a significant milestone: “We started off quite small back in 1984. We had a small block of salt marsh and it was more of a sanctuary then. It didn't have any visitor facilities, so roll on 40 years things have changed hugely.
“We just celebrated the fact that we've now got 100 volunteers and we've got 17 members of staff. Back in the day when I came here in 2000 it was just me. Annual visitor numbers have increased from about 5,000 to over 40,000. We’ve put parking in and we've got fantastic wildlife habitats. We now have more nesting waders here than any other RSPB reserve in England. We've developed a really nice suite of wildlife paths to enjoy walks - it's just a really nice quiet, peaceful place.
“We're improving things like accessibility all the time, so we've now got mobility scooters people can hire for free.”
John said the visitor centre and cafe had widened the appeal of the reserve as a destination for keen bird watchers and families.
He said: “It's a special place.”