If it rains in Lekeitio, there´s a nice walk to the Santa Katalina lighthouse, flat and ending in a very nice place with great seaviews, about half hour walk from the town center. You can also climb to the Kalbario mountain, the path starts very close to your hotel, for wonderful views. And if it´s a day with wavy sea, the show is at the "Tala", the end of the port, where the waves hit very furiously and they reach high altitudes, it may even be a bit risky. But this does not happen every day and our rough sea is not always rough. Expect any kind of weather, but it´s the Atlantic coast, green and mountainous, and quite rainy. I used to spend my summer holidays as a kid on this beautiful town.
In Getaria, apart from the great grilled seafood restaurants, there´s the Balenciaga dress museum (this extraordinary dress designer was born here), and there´s a nice monument to Juan Sebastián Elcano, the first person that circumnavegated the world. Also, some "txakoli" (our distinctive Basque wine, one of them) wineries at walking distance that can be visited on appointment.
I do not think water temperature will be nice in April, it´ll be too cold yet...even in August it´s normally a bit chilly.