The first clause of this sentence in Greek is actually a participial construction, and the second clause (when they saw Jesus walking on the water) is the main clause. A similar restructuring is found in Jerusalem Bible: “they had rowed three or four miles when they saw Jesus walking on the lake….” In Greek this verse begins with the particle oun (see under 2.18).

In Greek the subject of this sentence is “they,” which Good News Translation makes explicit as the disciples.

Three or four miles (so also Moffatt, Revised Standard Version, Jerusalem Bible, New English Bible) is literally “twenty-five or thirty stadia.” A “stadium” was about 607 feet. In languages where the metric system is better known, this distance may be expressed as “five or six kilometers.”

Saw is literally “see.” In Greek the present tense is often used to enliven a narrative, although the action is in the past.

The Greek phrase which is translated on the water is similar to the one in verse 16 which is rendered to the lake. Consequently, one commentator suggests that the phrase in verse 19 be translated “by the seashore.” That is, the disciples saw Jesus walking along the shore of the lake. However, it is obvious that John intends a miracle here, and most translators have the equivalent of on the water. Moreover, as the last part of the verse indicates, Jesus was coming near the boat, something he could not have done had he been walking along the shore three or four miles away.

It is possible to punctuate this verse in various ways, but no real difference in meaning results. Revised Standard Version and New English Bible put a full stop after “boat” and connect the verb that follows with verse 20: “They were frightened, but he said to them” (Revised Standard Version); “They were frightened, but he called out” (New English Bible). Good News Translation puts the full stop at the end of verse 19.

Some restructuring of verses 19 and 20 is necessary because there are so many embedded subject-predicate expressions. Note, for example, disciples had rowed, they saw, Jesus walking, Jesus … coming near, and they were terrified. The first subject-predicate expression may be the temporal setting for what immediately follows, for example, “After the disciples had rowed about three or four miles, they saw Jesus.” It is possible to conclude these two clauses with a full stop and begin again with “Jesus was walking on the water; he was coming near the boat.” The final subject-predicate expression may then be restructured: “therefore they were terrified.” The translator must take care that the reader does not misunderstand the reason for the disciples’ fear. They were not concerned for Jesus’ safety but were awed by the miraculous character of the occurrence. The parallel account of this story in Mark makes explicit what was going through the disciples’ minds: “ ‘It’s a ghost,’ they thought, and screamed” (9.49).

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .