Not strictly Lefkada, but I just had to tell people about these brilliant cruises which start from Preveza -- only an hour from Nidri or half an hour from Lefkada town. If you want a great day out, this is it. The cruise is within the Amvrakikos Gulf and you're virtually guaranteed to see dolphins, we saw lots and they were very close to the boat, sometimes right under it. The cruises are run by two young scientists who are passionate and very knowledgeable about the environment. You'll see coasts and islands that most Lefkada-based tourists never see, you'll learn about the local eco-systems, wildlife, traditional fishing methods, etc, you stop at a nice taverna for lunch & a swim, and you get free cold drinks & snacks on the boat. It's brilliant!
The cruises only run when they have enough people and when the weather's right, so you need to book in advance by phone or email. There's plenty of information on their website and Facebook page, but here are the contact details:
Lekkas Vasilis & Gigi Venetia
tel : 0030 2682041992
mob : 0030 6973395839, 6975067399