In the winter months if you follow the beach access road past the PAN de PLATANO (banana nut bread shacks) past the military base and then get out and walk upon the beach at sunset be prepared for an all-out assault on your flesh.
The highway south toward Sta Cruz and Las Varas has significantly fewer jejenes. Because there is a lot less brackish water. There are few jejenes on the waterway to La Tovara because the water is less brackish. See the big blue pipes coming out of the hillside at La Tovara spring? That's the municipal water supply.