Lewis' friend Claire Brooke told ABC that she and Jack were at the lake to celebrate a friend's birthday near Children's Fairyland; some of the crew were hanging out on the grass by the lake, while others were climbing trees.
ABC reports that the three people fell off as Lewis jumped to grab the branch, which snapped off the rest of the tree, and forcefully struck his head. One witness said he tried to give Lewis CPR, but stopped once he believed that his neck had been broken.
"There were 3 people sitting on the branch. Jack jumped up to hang on it and it fell," said Brooke.
The tree has since been removed, and public works crews are examining it to determine a possible cause as to how the branch broke.
"There’s no type of malice in his death," Oakland police Officer R. Brown told the Chron. "It's just a tragic accident."
Oakland Mayor Libby Schaff said in a statement:
Yesterday's tragic accident was a heartbreaking loss for our city, but most especially for the family and friends of the young man who was fatally injured in an accident involving a tree at Lake Merritt. I join with Oaklanders across our city in expressing my deepest sympathy to the family and friends of this young man who was taken too soon.
Friends left flowers, condolence cards, and mementos at the site where the tree branch snapped. You can see more photos from the impromptu memorial on Saturday over at the Mercury News: