Dear Tom,

As you know, missionaries serve under regulations that would be considered rather stiff by those who are not acquainted with the work. However, as they are called on the Lord’s errand, and their service is so vital to the eternal salvation of our Father’s children, they are encouraged to dedicate all their time and talents to the work of the Lord. A weekly preparation day is provided, however, so that essential duties not primarily related to the missionary work itself may be accomplished. This is not primarily a recreation day, although conservative recreational activities are permitted and even encouraged.

However, not only is swimming prohibited, but also other activities that may be either dangerous or not within the spirit of their calling. Missionaries should be particularly circumspect about activities "on the waters", as there is indeed both scriptural and historic precedent for avoiding unnecessary exposure.

On 9 August 1831, the Prophet Joseph Smith, with ten elders of the Church, began a journey from Independence, Missouri to Kirtland, Ohio. The Prophet recorded the following about this experience in his journal: "Many of the dangers so common upon the western waters, manifested themselves; and after we had encamped upon the bank of the river, at McIlwaine’s Bend, Brother Phelps, in open vision by daylight, saw the destroyer in his most terrible power, ride upon the face of the waters; others heard the noise, but saw not the vision." Joseph Fielding Smith, Church History and Modern Revelation, Vol. 1, p.206

Following the recording of this account, on August 12, the prophet received the revelation identified as Section 61 in the Doctrine and Covenants. Part of that revelation refers specifically to the power of the Adversary "upon the waters."

Behold, I, the Lord, in the beginning blessed the waters; but in the last days, by the mouth of my servant John, I cursed the waters. Wherefore, the days will come that no flesh shall be safe upon the waters. And it shall be said in days to come that none is able to go up to the land of Zion upon the waters, but he that is upright in heart. . . . And now I give unto you a commandment that what I say unto one I say unto all, that you shall forewarn your brethren concerning these waters, that they come not in journeying upon them, lest their faith fail and they are caught in snares; I, the Lord, have decreed, and the destroyer rideth upon the face thereof, and I revoke not the decree. Wherefore, let those concerning whom I have spoken, that should take their journey in haste--again I say unto you, let them take their journey in haste. And it mattereth not unto me, after a little, if it so be that they fill their mission, whether they go by water or by land; let this be as it is made known unto them according to their judgments hereafter. (D&C 61:14-22).

We read that it mattereth not unto me, after a little, if it so be that they fill their mission, whether they go by water or by land. One could infer from the above that those who were on their mission at this time should not travel by water, but that after their mission they could travel either by water or by land. Also, we read that the days will come when only those who are upright in heart would be able to journey on the waters. These are not the only dangers that could befall those who are not upright in heart. Those who persist in disobeying the Lord’s commands would eventually loose the influence of the Holy Spirit and would come under the power and control of the Adversary. Alma tells us,

And they that will harden their hearts, to them is given the lesser portion of the word until they know nothing concerning his mysteries; and then they are taken captive by the devil, and led by his will down to destruction. Now this is what is meant by the chains of hell (Alma 12:11).