The Baal Shem Tov, or Besht —  the founder of Chasidism — 
met the soul of the Messiah during an ascent to heaven. 
The Besht asked him, "When will the Master come?" 
The Messiah answered, "When your wellsprings break forth to the outside!" 
(from a letter written by the Besht to his brother-in-law about one of his soul ascents) 

Tashlikh teaching

Tashlikh bim'tsulot hayam kol chatotam – You will cast into the depths of the sea all of their sins!

The practice of Tashlikh comes from a time when no one could imagine that human acts could deplete entire oceans. The vastness of the sea, its capacity to receive and transform, to cleanse all, to breakdown and replenish, this is what we evoke in Tashlikh ~ something that Walt Whtiman also wrote about in Leaves of Grass:

What chemistry!
That the winds are really not infectious,
That this is no cheat, this transparent green-wash of
       the sea, which is so amorous after me,
That it is safe to allow it to lick my naked body all
       over with its tongues,
That it will not endanger me with the fevers that
       have deposited themselves in it,
That all is clean forever and forever...

Now our appetites consume whole species of fish, though fish are our model and metaphor for unimaginable fecundity. Industries kill off reefs; oil spills entire coastlines. Our ways of agriculture wash ages of good soil into the ocean, along with pesticides and manure. The greatest earthly symbol of the infinite is reaching its limits in our generation.

Can we still recite Tashlikh, throw our bread into the water, without remembering that our sins literally spill into the ocean? If only our sins could be transformed so simply by rituals, but it doesn't work that way. We need to acknowledge this reality in our Tashlikh liturgy. A suggested addition:

"May the leavings of our lives and actions be like this bread, which cast on the water can become food and nourishment in the cycle of life. May what we take from the Earth be what can come to us naturally, like the grasses that first gave humanity grain, and unbiddingly, like the wild yeast.  May we repair our arc in the circle of life, so that what comes to us flows from what is enough, and what comes from us flows back into the great river of being that is ever created by the One Source of Being."

One could also add emphasis to the following line from the traditional Tashlikh: "They will not harm and they will not ruin or destroy anywhere in My mount of holiness, for [they will understand that] the Earth is filled with knowing YHVH, like the waters are covering the sea" (Isaiah 11:9). As in,

"May this act of casting away, of emptying ourselves of what has passed, become a beginning of filling ourselves anew. May we be filled with awareness that Hashem fills every hollow and space in this planet, just as these waters fill (this stream and this stream fills) the ocean, so that may we learn and teach each other how to live without destroying and ruining this world that is the source of our life. As it says, 'Lo yarei'u v'lo yashchitu b'khol har kodshi, ki mal'ah ha'arets dei'ah at Adonai kamayim layam m'khasim.'"

Another thing you could do is to add the Al Chet prayer for the earth to your Tashlikh (download it here).

The Whitman quote comes from a section in Leaves of Grass titled "This Compost" (see the continuation of the poem below). A broader question about tashlikh we could ask is this: in what ways could t'shuvah be like composting? How can our t'shuvah be regenerative for the Earth, for all Life, and not just for our own lives? Composting turns what people think of as waste into soil. In fact it was never really waste -- food scraps can always become food for other creatures and source material for rich soil. Unless of course you mix the food scraps with poisons, as we do in our landfills. There's so much more to say on this in the future, but just asking the questions can be generative.
________________________________________

The quote from Leaves of Grass comes from "This Compost". The poem continues:

...That all is clean forever and forever,
That the cool drink from the well tastes so good,
That blackberries are so flavorous and juicy,
That the fruits of the apple-orchard, and of the
       orange-orchard—that melons, grapes, peaches,
       plums, will none of them poison me,
That when I recline on the grass I do not catch any disease,
Though probably every spear of grass rises out of what
       was once a catching disease.

Now I am terrified at the Earth, it is that calm and patient,
It grows such sweet things out of such corruptions,
It turns harmless and stainless on its axis, with such
       endless successions of diseas'd corpses,
It distils such exquisite winds out of such infused fetor,
It renews with such unwitting looks, its prodigal, annual,
       sumptuous crops,
It gives such divine materials to men, and accepts
       such leavings from them at last.

Design in progress © Rabbi David Mevorach Seidenberg 2006