water no longer blocks light

When building on top of the ocean, I placed torches, after awhile I noticed that a large section of the ocean underneath me was completely lit up. I tried to remove the torches as well as the blocks that I added but the lighting didn't go back to normal. Currently, the light level is 15 in a large section of the ocean, when there should be about 40 blocks of water blocking the light. I couldn't replicate in creative.