Abby and Connor are standing thigh high in the reservoir with the creature circling them. In the first part of the scene the creature is clearly seen above the eater, All other parts of the scene it appears that the creature is swimming in deeper water.
At the reservoir, Connor tells Nick that the water depth is 40 cm lower than when he 1st measured it (supposedly at the same location) -- when it should have been consistent. He deduces from this fluctuation that the reservoir is no longer a reservoir but a tidal lake. with water flowing out via the anomaly.
Problem is, when he tamps the measuring pole to demonstrate that the level is below his tape marker on his measuring pole, the tape marker is clearly above the level of the dock on which they are standing. If the water change is tidal in nature, the floor of the reservoir/tidal lake would NOT have moved to cause the fluctuation.
When Helen and Cutter meet in the past, she refers to the anomalies by that name. Since she had been missing presumed dead for fifteen years, there was no way she could have known that technical term which Cutter had created after she disappeared.