The park consists of two salt lakes: "Salina (Laguna) de La Mata" and "Salina (Laguna) de…read moreTorrevieja" (pink water). The area has a status of birds protection zone.
Salina de La Mata (green/blue water) is great for walking, running, cycling and birds watching. The information center of the park (aka "Vistor's Centre" or "Centro de interpretación Parque Natural la Mata-Torrevieja" in Spanish) is located here: 38.025134, -0.658438.
Salina de Torrevieja (pink water). You can get down to the lake to swim and bathe. Drive to Calle de las Lavandores (37.996916, -0.700556), park there, walk towards the lake (100-150 m). The salinity level is very high, you can float. Mud is in abundance. The best time to visit is from June to September. There's no infrastructure
Update June-10-2017. I wrote a blog post about one of the two lakes (Salina de La Mata), check it out: http://andrewcherkashin.com/salina-la-mata-torrevieja/