I'd heard of this beach before and pictured it as being much more difficult to access and more primitive than it is. You turn into the Blue Bay road and the first guard is right there near the highway. He only wants to see the drivers ID so he can take your name and know that you are going to La Vena restaurant. A second guard is near the hotel and you tell him you are going to La Vena. Drive past the hotel and along the beach, around the hill and you'll come out at the river mouth. Park anywhere from there to the restaurant.
About 20 of us went last Sunday in 4 cars. Brought our own food, drinks, a tent and tarps for shade and beach toys for us and the kids. Not only is this a beach much like Tenacatita but it's also a river mouth. The river is cross-able near the ocean and swimmable upstream. Someone said snorkeling was pretty good but there were a bunch of 'rays' in one area. One woman walked around the point and came back with a good sized bag of oysters. A really great day with lots of fun. Nice restaurant for beer and food, 2 public bathrooms with showers and places for your garbage. Great place to spend a day.
After we got back I wondered what the source of that river was because it is no small stream, at least at this time of year. There are no rivers that cross the highway anywhere near this area. To the south is Boca de Iguanas and to the north is Tenacatita. I asked on a few message boards but nobody knew. I eventually found on a Tomatlan site a reference to "La Vena" being an arm of Rio Purificacion but how did it get so far south. Then I found a .PDF file on a study of the area from the University of Colima and embedded in the study was the map below. It turns out that Rio Purificacion turns south just south of Tecuan and north of Tenacatita, forms the Tenacatita lagoons, and then continues south to come out at the north end of the beach by Blue Bay. That was my detective work for the week.
Blue Bay Hotel
Blue Bay beach
La Vena - Rio Purificacion
Setting up camp
The map showing the river course