In short, yes, there is.
The former is transitive (can have a direct object), whereas the latter is intransitive (used without a direct object). In fact you can say that the latter is the same as the former with "self" as the object (the postfix '-ся' called "reflexive" postfix, formed from "себя" = "oneself").
Here is the verb "плескать" with a direct object:
Днепр сердито плескал волнами.
The verb "плескаться" can be used in different shades of meaning. From the recent news:
Бегемот-малыш с удовольствием плескался в бассейне зоопарка.
На северном полюсе Марса когда-то плескался океан.
The first sentence, the baby hippo splashed with pleasure in a zoo pool. In the second, an ocean splashed on Mars' Nothern pole some eons ago. Both mean (in Russian) that the subject "splashed itself".